I am indecisive about choice due to room size

My opinion (which is worth what you payed for it) is that the Sonetta VIIIs are going to be a really big speaker for that room.  I don't think you will gain anything by moving to the larger speaker in that small of a room. 

I would look to step up to a higher quality speaker rather than just a larger speaker.  Not sure what your total budget would be but that would be my first priority.  

Not sure what speaker size you are considering, but as everyone here on audiogon knows  my opinion = bigger is NOT better.
Especially if the listening room is limited size,,,12x12,, ceiling 8 ft?
12x12  x 8 is limited,,,12x12 with say a  16 ft ceiling, now you have options. 
IMHO smaller the speaker = superior  the sound,,,let me rephrase that,,, the bigger the speaker = less  chances at high fidelity... 
Been around audio now 40+ years, I know what I am talking about
You must be new at this hobby.

agree with what has been said

bigger NOT better in a small room... key is right-sizing

Adding bass.... not an upgrade.

What I would do, have your room professionally treated by GIK. If you haven’t already, it will balance your bass to mid/treble energy better, in addition to improving clarity and imaging.

Do that long before you think about switching speakers.

I cannot tell you how many people do this and discover how much bigger their speakers sound. 

I'm in a basement space which is bigger than your room but with low ceilings. It absolutely could not accommodate tower speakers -- Focal 836, Martin Logan ML 60s. Bookshelves with a sub was the ticket. Easy to play with placement, too.