It sounds like you have done your homework. Your husband is lucky to have you. It seems he is in tolerance, meaning the drug has stopped working and should be tapered very, very slowly. It probably won’t be easy, but he can heal his CNS with a very slow taper, clean nutrition, moderate exercise, coping skills and support. Supplements are not always recommended because the CNS is so stressed and over-sensitized. If you try any, go very low and very slow. Most people steer clear. Functional medicine is not necessary if they are just selling supplements. Many people end up having to taper off the supplements! Just eat a clean, plant-based diet and watch for histamine intolerance.

I’d recommend looking at the following link and any other info the site has to offer. Benzo Warriors on FB has every other weekly zoom meetings (Sunday nights) for caregivers of those tapering off of benzodiazepines. You could join that group for more information, but I would recommend that you not read too much into the posts as many are pretty scary. A lot of people have been cold turkeyed (rapidly tapered off) these drugs and are suffering horribly. Those who are tapering slowly and have good support do much better, but it’s still pretty tough for a lot of people.
https://www.benzoinfo.com/ashtonmanual/
This is a highly regarded site and responsible for getting the black box warning for benzodiazepines.

I wish you the best and please, if his doctor insists on a quick taper, tell them you’ve changed your mind and start hoarding pills. Most have given up on their doctors for anything more than a prescription. That is critical. Doctors do not know anything about slow tapers. It’s not in their education.

Best to you and your husband