Does anyone have experience with the replacement seat foam offered online? I'd like to replace the driver side bottom seat foam because it has flattened, and not sure if this is an easy replace or not.

Try typing "replacing seat foam" in the Search box. There many previous threads on the subject, perhaps you'll find an answer to your question there.

I like whatever foam/layering toyota uses with their seats in modern cars, GM and Hyundai are fatiguing.

I rent a lot of cars and also do some very long commutes.

I just drove 1000mi non-stop in my S2000 on Saturday so my butt speaks with authority.

Foam is relatively simple to replace, remove seat, take back off, there is a cord sewn into the bottom edge of the seat cover. The metal frame has metal prongs which go through the seat cover and over the cord. Bend the prongs up and remove the cover and you are ready to replace the foam. I don't think factory foam is but there is reproduction foam available. I know that Classic Datsun Motorsports in Vista, CA offers it.

jlp

I just picked up the MSA replacement seat foam inserts. I'm still waiting on my seat covers, however I can tell you that I'm impressed by the quality of the MSA inserts. They are very dense, heavy and nice feeling. The molding is top notch. I'll reserve final verdict for when I get the covers in and try it out, however I think it's going to work very well.

I did my seats with the new foam and leather from MSA. I thought that everything turned out fine except that now my head is kinda close to the roof! The seat foams are nice and dense, so I may have to adjust by removing a little of the springs in the seat bottoms. FYI - You can see my seats in the my Albumz(link below).