Vals are like grass or hair-cut the tops and it will grow back so them getting tall is not an issue, they'll rail on the surface until you trim 9then regrow).
"Moss" balls are marimo and not a moss-its an extremely slow growing form of hair algae-a tank packed full of them won't make a dent in nitrates so they should be considered just decorative.
Crypts take a while to grow tall and the leaves will just float on the surface if they get there-you can always trim leaves that get too long.
Anubias is another easy plant option-nana and petite being common small kinds, golden is another variation that won't get too big for your tank.
IMO its better to have plenty of plants than using rocks or resin decorations-anything rough can rip up betta fins.
Excellent, thanks. I'm curious about your vals comment -- someone else just suggested that perhaps I *shouldn't* be cutting the tops (they're in my 29 gallon tank at work, along with the crypts), and the prior owner cut them as well, so that is what I've been doing. Unfortunately, they get brown at the tips and more than a few strands start dying back. Other possible causes for their somewhat poor health could be lack of fertilizer, and age of plant -- they're in two huge clumps and I wonder if they shouldn't be separated and replanted. I'm not even 100% sure they *are* vals, given that I don't see them sending out runners or taking over more of the tank, as I've read they do. (to clear up confusion: this tank was donated to me/my workplace when the current owner decided he was done with aquariums -- their are very mature plants in there, a healthy cherry shrimp (?) colony, and a few leftover fish in it...I'm still learning how best to care for it!). This post is supposed to be about poor Herbert, the betta, though! lol
I could just go with my marimo balls (sorry, every time I call them that, someone says, "what? you mean those moss ball things?"), and some juvenile crypts as well as the vals (maybe an anubius petit nana, if I can come up with something to attach it to), I just wasn't sure about actual betta preferences with regard to hiding spots, glass reflection/flaring issues, resting preferences (thought the tank is not a "tall" style, so that probably isn't an issue) and the like. If I'm going to buy and arrange things for him specifically, I wanted to make sure to do it right. I will avoid any sharp/non-smooth ornaments/rocks/wood, for sure. I just don't want to make his tank too boring for him!
If I'm going to do a significant number of plants, I need to think about fertilizer. I was thinking about putting some sort of dirt under the substrate, but that opens up a whole OTHER can of worms, as it is apparently more complicated than buying a bag of potting soil? I am not ready to make my own dirt (nor do I have the space for it), and I am completely happy with low-light/low-tech plants, so I don't even know if I should bother with the dirt thing. Maybe I need to just get a liquid fert like the Thrive everyone talks about, or that green-something that the Aquarium Co-op guy sells in all his youtube videos. I think I read that crypts need root tabs if the tank isn't dirted, though? ...seriously, I'm probably just overthinking this whole thing...