Have a search on here for Poole Harbour and similar terms, and there's lots of threads about local launch sites around Poole/Wareham/Studland/Swanage/Weymouth, etc., and things to do.
I love just pottering around Poole Harbour, Brownsea Island, up the river to Wareham, and out to Studland and Swanage, no need to necessarily do massive distances if you don't want to. Obviously there's a 10kn speed limit in Poole Harbour between April and October, with 6kn in certain places year round.
Or if you're towing to launch anyway, you could consider going east and into the Solent - loads of places to explore if you launched somewhere there on the mainland side between Lymington and Portsmouth. Solent launch sites are fairly well discussed on here as well if you have a search.
is another reasonable starting place for some research, although I don't believe it's necessarily super up to date.