I think you'll get better results with two subs, not just one.
You might be able to do that if you buy used.
Two subs, each one beside each main speaker, worked wonders for my system.
Subwoofer Suggestions
About 5 years ago, I put together a system for my college-bound son. Started with gifting him my restored Pioneer SX-950 (85wpc) receiver, then purchased B&W 607 bookshelfs and a Rega 1 turntable. Nice little system.
He's been in between job assignments recently, so all his gear is now set up in my listening room. The 607s sound great, but i think they could use the help of a sub. In all my years with this hobby i have never used one....so i need some suggestions, especially where/if they are compatible with a vintage receiver, what wattage is appropriate, etc. Any specific brand/model suggestions will be appreciated. Max budget is $600.
Thanks!