I would say most black teas would work, though maybe aim for a mid-tier rather than the cheapest (if you can afford it). I recently switched to an organic loose leaf black tea, that I really like. I don't find it crazy expensive since you're only using a few teaspoons of loose tea per batch. Positively Tea Company is the name, it's on Amazon and their website and they have sample packs if you want to try different styles of black tea to test.

As far as how to get started, I would recommend buying a SCOBY. I started my own from store bought raw unfiltered kombucha, but recently bought a new SCOBY directly. The difference was night and day. The bought SCOBY is way more active than the one I started myself. In hindsight, I wish I had just bought it from the beginning lol.

SCOBY:

https://www.amazon.com/Fermentaholics-Kombucha-Twelve-Starter-Culture/dp/B01N7S1CV5?ref_=ast_sto_dp

SCOBY + Kit:

https://www.amazon.com/gp/product/B07C86JGJG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Link to organic tea:

https://www.amazon.com/gp/product/B00GA91LJY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1