A few things over the years, other people are the best by when people aren't an option.
I have used Tascam BT1 mkii which had a function that could sort of remove the bass from recorded CDs, I'd play along with the bass free audio.
I used to use a Boss RC3 looper with a Boss FS6, which was fine for a bit but I grew frustrated with the delay when switching between different loops so I sold it.
I bought a standalone multitrack recording studio Boss BR1600CD, and would just make my own backing tracks.
If I feel like working on my soloing I'll pull up a backing track from youtube, and play on that.
These days because I prefer to just pick up and instrument and play without setting up gear, I try and figure out ways to carry the tune by myself, the bass is potentially a polyphonic instrument so I enjoy exploring that part of it. It is capable of basslines, chords and melody so I try different combinations, sometimes I'll sing the melody and play the chords and a bassline. It all just depends on the material, motivation and mood.
So I guess what I'm saying is, I have tried to use backing tracks, a looper, recorded my own accompaniment or tried to be a one man band. All the approaches are valid and each have their pros and cons. Try them all and see what works for you.