Betta Fish: Substrates?

Hi again,

I'm looking to upgrade my current 10 gallon tank to a 20 gallon during the PetSmart tank sale.

I currently have Fluval Stratum substrate. I'm assuming the amount I have is not going to be enough and im wondering what I can add to my substrate that's good for plants, but also not overly expensive. I do not mind paying a decent price. I've heard things about black blasting sand and play sand, etc. I've also heard how blasting sand killed tanks. I'm unsure what to go with

Any advice would be appreciated, thanks!

Picture of pretty boy photo bombing the camera lol