There are a lot of other keyboard recommendation posts on the forum if you want more opinions.
I've tried out a couple and landed on OpenBoard which fit my needs and didn't make it too complicated.
Some other keyboards I tried are Simple Keyboard, Florisboard, AnySoftKeyboard, and Gboard.
As for downloading them I use Obtainium as my primary "app store" since it downloads straight from github. I believe it can be downloaded through its website.