Enhanced Vanilla Trees by somerandomguy83
Just have to say I love this mod. I know STEP won't use the bigger trees option, but I absolutely love it. Aside from that, the textures are really beautiful and far superior to anything else. It also incorporates the snowy pine trees from SFO, as well as Realistic Aspen Trees (lots of optionals in fomod).
This + Verdant + Unique Flowers and Plants trumps SFO for me.
Seems suited for STEP as it is literally an enhancement of vanilla.