I have two boys, Arthur and Aithusa, who are in 5.5 gallon (cycled) and 3.5 gallon tanks, respectively. I've had Arthur for just over a month and I got Aithusa a week later.
Both tanks are heated, have live plants and caves, and are filtered. The filter in Aithusa's smaller tank is baffled and has minimal current. I'm still trying to figure out how to baffle the filter in Arthur's tank but he has an area of minimal current at the far end of the tank where some Anacharis reaches the top of the water.
I also use plain, organic Rooibos tea to add tannins and darken the water so they feel safer.
Both tanks get regular water changes and both fish seem active, love to explore their homes, and little Aithusa immediately comes to me if I put my fingers on the tank. Arthur is a little more cautious, but doesn't run away.
Both boys eat 2 pellets, 2x/day and are always happy when I show them the container with their food (HBH Betta Bites) and the occasional (maybe once a week?) freeze dried mysis shrimp, bloodworm or daphnia.
I've tried to do everything for them, and I'm hopefully just being a nervous Nelly, but neither boy has even tried to build a bubble nest, at least not that I've seen. Should I be concerned? Everyone always seems to tout a bubble nest as a sign of health and happiness.
I'm currently cycling another 5 gallon in preparation for a new boy, but if I'm doing something wrong I want to find out now before their health suffers.