Gaining Weight at 58 with Health Constraints

[BM58]

I am seeking some advice and ideas. I am 58 years old, athletic, and in pretty good shape. Back when I was 32 I had total colectomy surgery, meaning my entire large colon was removed and an interior pouch (called a jpouch) was created inside my body. In short, I take a biologic medication every 4 weeks as well as large quantities of Codeine daily to slow down my digestive system. Even still, I have chronic diarrhea, usually between 6 and 12 times every 24 hours.

I'm 5'9" and used to weigh around 160-165 when I played competitive hockey in university. Over the past 6 years, my weight has been in the 148-155 range. I have been strength training regularly for the most part throughout the years.

I am trying to find ways through training, diet and lifestyle to gain muscle / weight to be and feel stronger. I don't want to neglect my cardio but I really want to add muscle and size to my frame. Realistically, i'd like to get back up to 165 or even 170+ if possible.

Given my health situation, it seems like a very difficult task. I avoid dairy for rhe most part as it seems to aggravate me. So for additional protein supplements over the past years I have been sticking with the Vega brand or similar.

Any suggestions as far as training methods and diet would be greatly appreciated.