Hi there, and many thanks, to all who have replied so far -
I forgot to include the details of who who we've used so far - Blisworth Tunnel Boats and Grebe! We've had great days out with both, and will certainly return at some point to both of them. (Our daughter had her 12th birthday "party" on a Blisworth Tunnel boat, with Happy Birthday sung halfway through the tunnel! Problem was the candles on her birthday cake kept going out ). Anyway back to the present day, I think the bit about wanting multiple boats is, as Alan says, the killer!
Perhaps I've got persuade everyone (including myself) to get out of bed a bit earlier and travel further afield, because Lichfield is probably a bit further than I was originally thinking - will investigate it now.