Shaping Saarinen tulip chair cushions?  

egg recover in leather
i see you have covered an egg chair i have one i want to do but would like some advice before i start i have just completed an upholstery course but want to do it in leather

you need a good round ne...
you need a good round needle and a large thimble . and a lot of time .

latex vs urethane foam
Latex feels better than urethane foam. It's softer and more resilient than urethane.
I've seen urethane foam break down within a few years. Better grades may last a little longer but I would not buy it thinking that it will last 20 years or more.
The latex that is crumbling now was made decades ago. I wonder if the process has improved in that time to give us better quality foam? It would be worth asking about.
Also, latex dries out when exposed to heat and/or air. I bought a 60s sofa that was covered in naugahyde. The latex foam cushions were in perfect condition! I've seen other fabric-upholstered foam that was in great shape from that era and some that was completely dried out. I don't know why one was ok and the other wasn't, since fabric would allow exposure to air. It seems like the manufacturing process might have something to do with it, like exact processing temps or the age of the raw latex before it's processed. I know it has a very short shelf life before processing.
All this is to say that I wouldn't hesitate to use latex foam where appropriate. I wish I had a local supplier and that it was reasonably priced. I'd use it way more often in my upholstery projects.