Depending how small you looking SVS 3000 Micro would be good step up from the "bowling ball" and has better warranty/support etc. We have had few members cursing with the B&W after amp dieing. SVS SB1000 also at 500£ mark if you get AVF member discount. I believe it`s the smallest woofer in the market that has 12" driver and comes in three finishes to keep wife happy. Plenty of choices depending the critical dimensions/finish/what you looking from it..
As Conrad mentioned BK is good option if you want something small in real wood veneer finish, perhaps the DF model so the driver isn´t visible. Like a small furniture and cheap.