Searider on here (Duncan) did my survey through YDSA and it made a nice change to find a surveyor who knows what he is talking about and a jolly nice chap too. they have a good web site with lots of info.
In theory YDSA now have details of P22 stability test for 9 people so you shouldn't have to do this if you code it with them which might save a bit of money. However .....
Although the stability test is for 9 people I only coded her for 6 in the end because the weight of diving kit that would need to be carried as well, also the costs of lifejackets and liferafts for a larger number of people was just getting out of hand.
Hired a SOLAS B raft for the first year which cost £560 for a 6 man from Ocean Safety in Saxon Wharf, Southampton. Not the cheapest but they know what they are talking about and supply to a lot of local charter boats.