So you want to be able to play one-finger powerchords on both your thickest string, and second thickest string? Drop-D, but with one more "dropped" note below?
Try thick to thin G-D-A-D-G-B-E. Though, with the G on what's normally the low "B" string and the regular A above it, you can't do three-note one-finger chords, but just two note ones.
When I drop-tune on my seven to play drop-D stuff, I usually go A-D-A-D-G-B-E. This way, you still have a drop-D guitar but if you either 1.) accidentally or 2.) intentionally include your lowest string too, you're just adding a fourth below (or basically doubling the 5th above, as they're enharmonic equivalents).
Though, Drop-A works pretty well too, on it's own (A-E-A-D-G-B-E).
Also worth a nod for more Tool-like moments, A-D-A-D-G-A-D. It's a celtic/world tuning, generally, but with the added low A it absolutely kills for big suspended voicings.