Best musical sub to pair with Atohm GT1 SE bookshelf speakers?

Hi all,

I recently purchased a used pair of Atohm GT1 SE bookshelf speakers and while I am very impressed with the quality of low end from these speakers (low freq ext: 45 Hz), I think a good sub will definitely help make them sound much fuller.  

I am looking for a small budget sub, the smaller the better and appreciate any advise on recommended options.  Some details:

Source:  Naim Uniti Atom with music streamed via ethernet cable connected to wifi router (Macbook pro as roon core)
Power Amplifier:  Naim NAP 250
Cable: NAC A5

Musical tastes: Rock/Soft Rock/Blues - Pink Floyd, Dire Straits, Doors, Eric Clapton, Sting, Audioslave etc; Vocals: Norah Jones, Adele, Lucinda Williams, Beyonce, Sade, Joss Stone, Ray Charles etc.; some instrumental like Spanish guitar, Sitar etc. and very little jazz/classical

Room Size:  approximately 300 sq ft (27 sq mtrs) but open on two sides;  the speakers are kept about 7 feet apart and I have very limited options in placing the sub in the room (most likely only options are next to either of the speakers).

Where I live there aren't dealers for many of the products and internet delivery is not an option.  There is dealer representation for some brands (SVS, JL, KEF, Focal, Sonus Faber, Vivid Audio, Dali, B&W, Wilson, Monitor Audio, Dynaudio etc.) but unfortunately not for REL, Rhythmic, Velodyne.

I recollect reading good things about REL subs and especially that they are best suited for music which was my requirement as well as I do not intend to use this for Home Theatre at all. 

I am considering either the SVS SB-1000 or the REL T5i both of which are small in dimension although with very different specs.  Also, as I don't have an REL dealer here I would be looking at importing it which would mean I'd  have a tough time returning it if something went wrong.  I'd also prefer to get the sub in a white finish to please the missus and help match the decor in the room.  Both the SVS and the REL are available in white which doesn't seem to be the case for many other companies subwoofers.

Appreciate any advise on whether the SVS SB-1000 is as good as the REL T5i (or perhaps even better) and will be a good match for the Atohm GT1s which I think are a very good quality set of bookshelves.  And if there are any other alternatives that you'll can recommend, I will try and see if I can find dealers for those brands too.

Thanks!