Yes, bridgesii seem more prone to rot, in general not just the roots, than the other species are. This is just based on anecdotes and watching my own cacti but I believe it's true.
I've been using about 15 percent coco coir, 15 percent peat moss , 10 percent compost and amendments ( alfalfa meal, kelp meal, bone ,meal, azomite, worm castings, malt barley and wheat seed and more recently chicken manure and crab and lobster shells) and the remaining 60ish percent is pumice and/or perlite... Depending on what I have and how much money I have; pumice is way more expensive for me. Some people are able to find it locally in which case it may well be close to the same price or maybe even cheaper than perlite.. From everything I've heard pumice is preferred for aeration , as opposed to perlite or some form of gravel etc, and from what I can tell it is definitely superior ...
I'm not sure on the exact ratios and what you'll want to use yourself will vary and depend on your climate and how much water they are getting etc.