I've been using the Sony HVL-F28RM with my a7CR for about 6 months now and it's been excellent. Perfect size match for the compact body while still having enough power for most situations. Battery life is solid and the radio wireless capability is convenient when you want to get it off-camera. If you're looking for something even smaller, the Godox TT350S is a budget-friendly option that won't overwhelm the small form factor of the a7CR.

Godox flashes like V1 S.

I use this one. love it.

Godox flashes are recommnedd.