I have not seen one of those bouncy seats for bigger kids but would sure love one for Langan. She is a big fan of bouncing!!

If your son can support himself standing, then the trampoline we just bought might be a great thing for him. It has a wonderful handle that is the perfect height for a 4 year old. Langan holds onto the handle and jumps like a wild thing. I bought it at One Step Ahead (Onestepahead.com). It's not a SN catalogue and the trampoline was about $200 cheaper than almost the same thing in a SN catalogue I have. It wasn't exactly cheap ($130ish) but we got it as a gift for Langan and she's getting her money's worth out of it.

Here is the link with a picture of it. http://www.onestepahead.com/product/117/367766/117.html

Just wanted to throw that out there! I'll be keeping a close eye on the responses to your post, in case there is a bouncy seat I didn't know about!