I had this exact situation arise a couple of years and, after a brief flirt with a couple of options, settled on a Phil Jones Double Four. Utterly fantastic sounding piece of kit - and I play 5ers pretty much exclusively so the sound of those lowest notes was key to me. It handles my B string with ease (I even run octavers and synth sounds through it) yet it’s the size of a shoebox. Proper, full bass sound.
No idea how Phil Jones have managed such a feat. In my opinion it’s the best truly small amp on the market if practise and small jams are your primary concern. It’ll happily fit on/under a desk, on a chest of drawers, under a bed - pretty much anywhere. Just don’t expect to be doing serious gigs with it as it does have a limit.
As a side note, it doesn’t have any overdrive or other effects on board (since you say you’ll use it for guitar too) so you’ll need to plug pedals in if you want that kind of thing.