I have a cool little unit that is about the size of a pack of cigarettes, has clean, overdrive, and distortion, vol and tone, and stereo chorus,headphone, and line in/out for $39 at GC Called Rock-it.
Actually it’s kinda cool to look back at the suggestions from 13 years ago... nowadays there are TONS of tiny headphone amps to choose from, but very few at that time.