Chatsworth, of course, is wonderful, rocky. You need a whole day (about two hours for the house and the rest for the "garden"). Bolsover is very interesting historically but not a great deal to see. Crich is a must for anybody remotely interested in transport, or anyone who likes a "step back in time". They have about 50 trams from all over the UK (and a few from abroad). About half are runners, the rest on static display, and all in superb condition. They run three or four each day and you can travel as much as you like up and down their track of about 1.5 miles. They also have a couple of buildings (Derby Assembly Rooms and the Red Lion pub) which have been removed from their original locations and rebuilt brick by brick at the museum. An absolure must!
Sorry David, hijacked your question. Hope you find somewhere suitable in Dorchester. A fine town which I visit from time to time. Don't stay there as I have relatives nearby in Bridport who put up with me - yes, put up with me, not put me up :-). Beware of Premier Inns and Travelodges. I use them a fair bit and cannot recall one having a shower. Not sure about their disabled rooms, though.