If you need both pitch and mod wheels, you'll have to step all the way up to a PSR-s710 (or s750, etc.) There are some tiny PSRs like the PSR-E323 that you could buy for $100 on eBay. But no pitch/mod.

Some of the mid-line models like EW-410 and PSR-s670 Edit: PSR-s650 have only one modulation wheel.

All of these PSRs are bigger and thicker than they would need to be for your purposes because they have speakers and at least some arranger controls.

There are tons of controllers on the market, I guarantee one of them has the keybed and controls you want in a smaller footprint. My $.02.