I kept all of mine in bare bottom as well, much easier to keep clean, and with FH cleanliness is very important, both water and filters. The less bacteria the better. I also kept my temps cooler than most, 78-79 F. Bacteria tends to grow faster in warmer water, especially certain pathogenic bacteria such as columnaris aka duck lips.
As far as variety, as long as the fish is eating eagerly, most commercial foods already contain a "wide variety" of raw ingredients. If one wants to feed 2 or 3 different pellet brands that's fine, I just tend to avoid high protein foods (as already mentioned previously by other members) and I avoid meaty foods, including fresh/frozen/freeze dried. Others may disagree with my approach, but the KISS (keep it simple stupid) has always worked best for me when keeping fish that are known to have sensitive gastrointestinal systems. That includes numerous bloat prone cichlids, over many years of keeping cichlids. Higher protein is fine for very young fish that have much higher metabolic rates, but your fish is well past that point now, where a more maintenance level of protein/fat is more ideal. Similar from switching a young dog from puppy food, to an adult formula.
Make sure to update this thread over time, I'd like to see how he eventually turns out.
Good luck!