I've been using Simple Keyboard, which seems to be what it says on the tin. Not a lot of features, doesn't make my phone sad. (In today's android, 2GB is not enough memory, saving some ram on the keyboard makes my launcher less likely to swap out when it's in the background; I wish I was overreacting)

https://play.google.com/store/apps/details?id=rkr.simplekeyb...