My LONG car seat obsession

I have a slight obsession with car seat safety. I'll start by saying that the PA state law says that a kid is to be rear facing from birth to 1 year old AND 20lbs. There is talk that they are trying to make it even longer. After the rear facing position, they are suppose to be restrained with a 5pt harness seat to 4 yrs and 40lbs. After that, they have to be at least in a booster till 8 years old. We continue to use a 5pt harness though because it is safest and with our cars, we can latch it in.
I just saw a thing on the news the other night about a kid who was 5 dying in an accident because the seat belt failed. It was used properly but sometimes they fail in an high impact accident. Obviously that is out of our control, but why run the risk if there is a seat out there that your kid can be safe in for the longest possible? Just my thoughts. So here it goes....
When I was pregnant with Kristopher, I honestly had no clue about the car seats. I knew that they had to be rear-facing till a year, and didn't really put a whole lot of thought into it. My mom got me a graco travel system with the cutesy little carrier car seat and I figured that would last a year because everyone else used them a long time. HA. Then I realized that our seat was good for 26 inches and 20lbs. I never realized they outgrew at a length. I thought it was just by the weight because it was the only part advertised. So, at his 2 month wbc, he was 25 inches long. I did a little research and discovered that he would not be safe in that for much longer and panicked. We got a convertible graco seat and all was well again. By the time he was 8 months old, I was reading more and more about the seats with those overhead shield things not being very safe. Well what do you know...that's what we had. It was one of the last made of that kind of course. I did my research and was told the "best" was britax. We got a britax marathon which claimed to be good up to 65lbs. Again, I forgot that they can max out at a certain height but figured 65lbs was way way off and it would probably be the last seat I'd need to buy. Wrong again. Turns out my kid is not only tall, but long up and down so he outgrew that seat around 4 and half. While typically most people would say it's time for a booster, I'm paranoid. I saw this video a few years ago and am scared to death of putting him into a booster. It is another case of the seat belt failing.
So, last January when it was getting harder to get him in and out of the seat, I went searching for the car seat that they mentioned in that video. A britax regent. We went to babiesrus and tested it out in our car. The thing was freaking huge. I have an explorer with a fairly large back seat and the thing took up the entire spot he was usually in, plus part of the middle seat. And it shoved him up against the back of the passenger seat to the point of not being able to get in that side. So instead we got a britax frontier for my car, and a graco nautalis for my husband's car. Now, the britax I figured I'd love because of the first one we had. I do not like it at all. It's still big and bulky, he has a cup holder that his cups stick in and cups from while we're out spill if he's not super careful. There is no way it's going to work really nicely as a booster some day. And it's a pain in the butt to install. It takes up a little more than one seat so it's hard to fit others in the car with us. The straps are not "no tangle" like the ohter britax was, even though it claims to be. And he says it's not as comfortable. It is safe though. The graco I really like and it has a cup holder that is like one made for a car. It will work great as a booster some day and fits so much nicer in the cars. He is able to get in and out of it easier and claims it to be his favorite. I actually swapped car seats with my husband this weekend so we could take my parents along on a day trip and everyone fit easier.
Now the whole reason behind my post today is my boy is growing yet again. My mom has a seat in her car because it is easier than swapping these huge seats anytime he goes with her. She had a cheaper Safety 1st seat that he has offically maxed. So I'm switching my britax to her car once I get a new seat. She can use it for him, and also my niece in a few more months when she turns forward. It's super easy to adjust the straps and go.
While the graco was out, I moved his straps up. He's officially at the top harness straps. It gives him another 2 inches up and down (sitting to shoulders) and then he's outgrown that seat in height. He is 48.5 inches tall now. He's 47lbs. So he still has a while till he maxes out that weight, but obviously he is not going to make it to the max of 65lbs in that with the way he is growing. I've been trying to decide what is best. I could just remove the straps when we get to that point, and he will be in the booster. I'm guessing I still have another year of that working. He will max out any 5 pt harness seat by the time he hits 53 inches.
Right now my choices for another seat for my car is either another graco, and he will use the booster part to get him through to that 8 year mark, or get a radian, which is a more compact car seat up to 80lbs (still same 53 inches I believe for the harness...) I would still run into the case of having to buy an additional booster but maybe I'd need the radian by then for another kid....
If I'd have known all this to start with, I would have bought a radian after the infant seat. That would have saved us a lot of money and been able to use till 6 yrs old at least. If I didn't have a giant kid, I bet it would last the full 8 years! Either way, I'm just not sure if I am ready to stick him into a booster and run the risk of a seat belt failing. They may be expensive but you really can't put a price on your kids safety.