Have you considered ergonomic / butterfly / trekking bars? It will provide more variety of hand positions (particularly fore and aft) than a flat bar.
A fancy one from Wall Bike
They also sell non-hinged ones made by Acor and ITM for around $15 or £15 depending on where you live.
I recently converted to these bars (ITM model) from drop bars and I quite like them. Here's a picture of mine:
As you can see I kept my bar-end shifters, and mounted them using thumb adaptors. I find the upright posture is more comfortable. Good luck with your bars!