Adding subwoofer to Quad 12Ls

I have my audio system in a large room, 15' x 30'. The Quad 12Ls started in a smaller room but have been doing a fine job in this big space for awhile now. They are matched with a Plinius 8100 integrated, and I listen exclusively to vinyl.

Should I add a subwoofer to this system? If so, should I stick with a Quad? or would it better to just invest new speakers?

I have 22L's that I use Quad's subwoofer with. Also my bedroom system uses Quad.'s 5.1 Lite system that includes Quad's basic subwoofer. Both systems work, sound and integrate easily.
Thanks. Anyone else?
Yes, add a subwoofer. My 12Ls are in a bit smaller room than yours and they benefit greatly from the sub. I experimented with 3 different subs and found two that worked well (REL and Energy). Don't remember the model numbers but both were under a $1K....I currently am using the REL (T-1? T-3? can't remember). Very happy with the sound.