A bed and breakfast is often the better call in Poole, because the town's most interesting streets are residential rather than commercial.
Old Town and the Quay
Rooms in the Old Town put you inside the historic quarter, a few minutes from the Quay and the boats. Parking is the thing to confirm.
The villages
Ashley Cross, Parkstone, Hamworthy and Broadstone have guest houses that are quieter, usually have space for a car, and cost less.
See also hotels and self-catering.