Check out Aria’s AMB-50b. I’ve the fretless version and it has an acceptably (to me) round tone, volume and sustain, at least for what it is. Acoustic basses are rarely good for playing with anything other than one or two acoustic guitarist – it’s just so hard to get volume in bass with such a relatively small body.
I’d recommend staying well away from Tanglewood – thin and quiet to a fault, same as many of their acoustic guitars.
Have you tried Thomastik strings on your upright? I use them on my Aria and they really bring a lot to it – beautiful strings. Balanced gauges and a really full, loud sound. Very pricey for an upright, but there-or-thereabouts for normal normal strings (link).