All car seats in the US can be installed with a lap only belt, so that makes things easier! What kind of lap belts are they, the kind with a tail that you pull to tighten? If so, they are usually pretty easy to install seats with.
The big consideration is that you won't have top tethers when you turn your child forward-facing, and you can't use a belt-positioning booster with lap-only belts. So, it's probably best to keep your child rear-facing for as long as possible. How old, tall, and heavy is your child? There are multiple seats that rear-face up to 50 pounds and are quite tall, so many kids can rear-face until school age if needed. Let us know your child's stats and your budget, and we can give you more specific recommendations!