I would recommend staying in Purbeck as the area has a fair bit to offer. Start at Studland with the stone row, then a wander on the 'moor' to see the Agglestone & the Puck stone, next a short drive to Rempstone Circle (an absolute delight, an optional extra here is to climb the hill to the south to the barrow cemetary with all round views) then head south-ish for the Harp stone to finish off a nice wander?

Have fun!