What sort of hotel do you need 5*? Or something a little more sensible? Where abouts? In Southampton city centre you have the Grand harbour (has a pool) and the holiday inn in west quay road, both of which give views of southampton water and are very close to town quay and ocean village etc. You could always try Lymington, or maybe the river hamble both of which would enable you to get in close proximity wth boating and are closer to the Solent. There are a couple of RIB charter places on the hamble or better still a few members of ribnet live close by and may be able to help you if they can.
we used this company last year, a gift from a bearing rep:
Lets face it, If you get the right weather and a nice boat for a few hours, most people get hooked straight away. Your wife may well trade in the Peugeot before you get home!!!