Oddly, I’m still using Islabike saddles for my 9yo even though he’s been on a non-Islabike for 12 months now, because they are a good shape, reasonably light and very cheap (£15 IIRC). By 11yo, they may well be onto a smaller adult size though – it would very much depend on the build of your son. If interested, call them up and you can buy them direct. A fair few club racers are running the cheap, chinese carbon ones from eBay now, but I feel this is a bit cruel (even thought he pesters me to buy one every week!)
Regarding grips, I use these ones because they’re a good size (bit narrower than normal, quite thin), decent price and half decent quality. They do wear quite quickly, so bear this in mind, but we get at least a year out of a set.