Assuming I can convince my wife it is okay to get another pet snake, what should I get?

I have room for a 30x12x12 or a 36x18x12. Possibly a 30x12x18 or a 24x12x16. Basically your 20 or 20L, your 30, or a 29 gal.

I have outlets for heat pad, heat lamp, etc. I do not have any more room so it would have to be able to live its life comfortably in any of these tanks/enclosures.

I already have 3 snakes (2 corns, 1 BP), so keeping the food supply the same (F/T rats or mice) would be great. That is no cricket eating lizards. I'm not looking for anything aquatic either. Something arboreal would be awesome, but I'm not sure I could meet the height requirements. Maybe semi-arboreal?

I feel as though I could handle something moderately difficult. The only issue I would have is something that needed super high humidity. If the humidiy requirements are no more than a BP, then I should be fine. (Our base humidity is around 50% and I can bump it 20-30% higher for sheds). I can make it as hot as I want it seems. Ambient day temps of the house while we're at work are around 79F (saves on out A/C bill and the snakes love it!)

What I want is a beauty snake or a vine snake, but I just don't see that happening.

Any thoughts or questions?