I keep meaning to post this and I remembered while ignoring watching my 6 month old just lounge happily in her playnest. It's essentially a cloth covered inflatable ring, and they can go in it before they are sitting. You can prop them up in it or as dd2 is currently doing, just lounge back, toy all around her to hand. She plays in it happily for ages, as did dd1.
Mine is from elc I think (actually eBay) and Galt do one too like this. It's a bit of a monstrosity but it's only for a while and you can shove all the toys in it at the end of the day.
A definite recommendation. Just wanted to share my recipe for baby happiness leaving more time to mumsnet