Click here for information about getting to Bath
There is a great choice of accomodation in Bath. It is mostly excellent but can be expensive as supply doesn't really meet demand
Remember Bath is surounded by hills and so if you have difficulty walking it will be wise to check your accomodation is close to the centre.
The differences between these classes of accomodation are blurring. Some guest houses are more akin to hotels offering superb service.
See http://www.visitbath.co.uk/site/where-to-stay for a comprehensive impartial tourist office list. Remember that accommodation providers will need to pay a commision from your booking.
For a guest house - consider using the Bath Guest House Assocaion's clever site
Self catering can be an excellent option in Bath - even for just a few nights - Bath Self Catering Association is a useful site
Tripadvisor is helpful to many people. Remember that any odd looking extremely positive views or extreme negative views tend to be less meaningful than the overla picture you get. Hotels here. Guest houses here.