From what I'm hearing, this situation really is a "band problem" in disquise, and has filtered down to being a "bass player need to fix it" problem instead. Before you go down the road trying to buy your way out of a problem which may still not fix the tone/muddiness, volume, etc... the way that you think it will, I strongly, strongly, urge to have a band talk and to try to see if the bass signal can be run into the monitor and mains, along with the vocal. Of course, they can say, "why can't you just buy a bigger amp", and of course it's your money. But the "fix" for all this may indeed be "free" with just some knob tweaking and experimentation. I prefer free.
Practicing in small practice rooms, for better AND worse, is never going to be like some stages in terms of the sound that you are used to hearing. I know you want that comfort zone, but see if you can get a mix, via the help of the soundperson, to help it make the sound comfortable for you and the rest of the band. It IS the soundperson's job to at least try if you ask him/her!