Subwoofer recommendation

I have a listening room approximately 25'x25'. Until renovations had to be made (due to smoke from a fire) I was very happy with my sound.  Now, with the room emptier I'm feeling a lack of bass.  Can anyone suggest a good subwoofer that will add bass but not alter the basic sound of the system? I have wonderful modified vintage Dalquist 20 speakers
  Looking in the 1K-2K range.
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SVS PB13 Ultra
REL or JL e series
Second to the JL. They're powerful, but easily adjusted so that you don't overpower your listening space.
Vandersteen 2Wq - if you can accommodate its unique connection requirements.  I own two and absolutely love them. 
Ditto on Vandersteen 2Wq sub.
I've a sealed REL Strata 3 and prefer it over ported designs as it's tighter and faster so you might consider that factor.

I use 2 relatively inexpensive (bought used) RELs and they’re perfect. Can’t imagine not having those damn things….a Q150e and a Q108II.
Add a pair of Rythmik F-12G subs and be done. Excellent performance at around 1k. That's my biased 2c.
Thanks for all your recommendations.