I can thoroughly recommend B & b in Hamble Village called Compass Point-
Mike runs a great place right in the heart of the village and very close to all facilities including marinas.
Launching in the area , there a quite a few options from a free launch in the village on a public slip which is a tight squeeze for anything larger than 6.m rib but Mike would have to advice on parking and trailer issues and the opposite side of the river at Warsach public slip, then put car and trailer into car park for a fee. Or you could spend a load(25-£30) and launch from a great concrete slip at Hamble Point Marina, which would give you loads of parking etc and facilities and secure.
There are a few other launch slips further up the River you can find on http://rib.net/boatlaunch/
Another option is Calshot on the Western side of Southampton water at the Solent end, All these are very close to The Solent, Calshot you can camp at their site on the waters edge.
I am sure other ideas will follow