You are right to go with 61. Until council cutbacks in roughly 2004/5 (I forget when exactly), it ran along Sutton Road. Then Stephenson's reintroduced the number on a similar route, but using the nearby Bournemouth Park Road instead. Traditionally it was run by First and their previous incarnations, but was for a while operated by Arriva (in a rare period of them actually doing quite well, unlike now).
If you want to see a route that requries only one bus to run that changes model every day, the 61 is a good bet. It isn't unknown for it to have a Solo one day and a decker the next - in spite of SE having a 61-branded Dart...