What size subwoofer to get?

This question is for 2 channel stereo use 50/50 rock/classical music. I have floor standing speakers rated down to 35hz on axis and instead of getting expensive larger speaker want to look at adding "powered" subwoofer to slightly extend bass. Three models are available:
10" woofer 30hz
12" woofer 25hz
15" woofer 22hz
All these models have adjustable crossover frequency cut-off
50-150 as well as adjustable volume. What size is best to get, my concern is getting too much bass that is hard to dail back and becomes overwhelming. Or is it better to get largest subwoofer and not worry, volume control will be able to effectively tailor sound and control bass?

This is my first subwoofer so need some general advice from members who use them, thanks.