Frankly, for a lot of CQB stuff, pistols are just a far more sensible option, in fact, at some sites, having a rifle or SMG is actually rather clumsy and their use can even be forbidden in certain areas. Because of that, I'm going to try a G36 as a back up on a sling across my back (since it has a folding stock). The primary CQB weapons then being two pistols, one in a drop leg holster and the other in a 58 browning holster hung from a belt attached to a tactical vest.
Having had reliability problems with a CYMA electric Glock 18 (which resulted in me having to resort to a knife kill the other day lol), I've ditched the electric Glock and am using two springer pistols - a Glock 26 and a Kahr TP45 - with spare mags for both in the vest, plus some spare mags for the G36. Since neither pistol is semi auto, this makes the rate of fire slower, but I've no worries about reliability or running out of juice. I can cock either of them pretty damn quickly anyway. I may see if I can sort the reliability issues with the electric Glock and ditch the G36 altogether for CQB. The TP45 does 300+ fps, so that set up does still have some range.