Hi! I used to work for a specialty greens grower, and we grew, harvested and sold lots of micro greens for restaurants around town.
We bought all our seeds through Johnny's Seeds in Maine. They have a sprouting section, listing those that are good for microgreens and sprouting. We grew red chard, beets, arugula, radish, red mustard, sunflower, mizuna, tatsoi, maybe some others.
They're delicious, but I would say expensive to grow. We charged $10/lb wholesale. We would fill a flat about 2/3 with soil, make 4 rows, sprinkle seed, cover them, place them in the greenhouse, keep damp, water 1-2xs a day, depending on the time of year, and harvest them, cutting them when they were about 2 inches tall with scissors, rinse them. We'd sell a lot of mixed batches, kind of like a mesclen. We would throw the soil, roots and stems into the truck and dump them in the fields that we gardened. So, you use a lot of soil. I never used felt, but I guess you could. But you don't get the nutrition that the soil gives them. But I guess sprouts don't have that either.
Sunflower sprouts were my favorite. Delicious and sweet. I could eat them by the pound! If you check with Johnny's, ask for a commercial catalog. I'm looking in my home growers catalog right now and only see sprouts, not microgreen sprouts. It's the same seeds, just sold in 10lb packages, even 20lb for the sunflower.
If you grow them, see if you can sell some to the upscale restaurants in your area. They use them to garnish mostly. Mustards and radish have a strong flavor! A mix is very tasty. You could even mix your seed before you plant them. Most of them sprout at the same time, minus sunflower. Enjoy!
