If you can find one of these, they don't require a thumb. Pull the lever in for the brake, push it down to pull cable (up shift) and flip it up to release cable (down shift). The thumb buttons are on there to push the lever up for extra convenience. It's a 3x9 XT shifter from a while back, I found it on ebay for about $40 a year or so ago.
Looks like they're called dual control levers.http://www.ebay.com/itm/Shimano-XT-Dual ... 19dd2353c0http://www.ebay.com/itm/SHIMANO-Deore-X ... 3f25381848
Here's a link to my shifters on my bike on facebook. I couldn't get them cropped down to fit well into the forum. Let me know if you can't see them. There's 4 in the album: wide view of shifters, side view, actuating down, actuating up.https://www.facebook.com/photo.php?fbid=10201332560541264&set=pcb.10201332560781270&type=1&theater
The thumb button unscrews to come off as it's not required, tried it that way for a while but it was just too nice to have both options.
Not sure where you're located, if you're around Holland, MI I could show them to you sometime to see if they would work.
Otherwise, 1x9/10 seems like a good option.Edit:
Just realized this is what Redstone Liger mentioned.