Hello gardennut! That sure sounds like your plant has a nice caudex! Yes, when you repot you can raise the caudex to expose the lovely form it has below the soil line. I use cacti mix, compost, pumice/perlite. Got to keep it very well draining. Or use regular potting soil but add lots of pumice/perlite to make the media gritty and very well draining. Use a container about 2 inches wider than what it currently has, not too deep with drainage holes.
If your plant is still dormant right now, you can even do some branch pruning if needed or do some root cutting as well, if you just wish to re-use the same container it is growing in, but lift the caudex. Then just repot, do not water yet if it is dormant, just wait patiently for it to wake up. Got to allow the roots and branches to heal if it were pruned. That is one of the fun parts in growing this plant, the lovely caudex it forms.
Once the caudex is lifted a bit, give it time to be used to the sun, so position it in part sun/shade so the lower part that is now exposed won't get sunburnt, it will eventually get used to it and enjoy full sun later on.
