Call Marina Pool and Spa in Colorado (easily found via the Goog) and talk to Margaret. She *will* help you determine which robot will help you the best. And her prices are often cheapest we've found and considered a "brick and mortar store" so the warranties are longest avail.
Some credit cards can also extend warranties....check your card perks.
The S200 by Maytronics is probably a good one for you.
I have a Dolphin E10 and love it. It is designed for small in ground and above ground pools.
It's the least costly robot, that has an active (spinning) brush. It will not climb your walls, but
should do a great job on the floor and cove.