If you get a flat bar, you'll probably need a stem or extension to raise the bars to about level with your seat, I would think. Also, I'm a big fan of trekking/butterfly bars, myself! With some butterfly bars, you could probably use your current brakes and shifters on the inner or outer elbows, though I don't know how convenient that would be for your hands.

Oh, and as mentioned in the post below, while I was editing this, you may just want to stay with your current drop bars, and just look to raising the stem up and tilting the drops a bit upward, to give you a more comfy upright position without having to change anything else in your handlebar area setup.