Looking for a Car Seat Solution.

[elmo]

I have a 3 and 5 year old and wondering how people get there kids around now. The 3 year old is still not a problem,(can just use the lap belt in the back for her current car seat) but the 5 year old old grew the car seat that I could just use the lap belt...in the newer cars he sits in a booster seat that uses the lap and shoulder harness.

I know when I was a kid we never used seat belts that I can remember, but would the lap belt be safe enough or have people come up with other options other than putting in seats with intergrated shoulder harness? Or is there a child seat that would work with just the lap belt for bigger kids?

I know dumb question and leave them at home, but I plan to use it as a daily driver once the salt is off the roads and I get a soft top!

Thanks in advance!
Elmer