I would suggest looking at bikes that have a rack, or fittings for a rack, to strap your gear to, and anywhere between three gears (uphill, flat and downhill and 30 gears. fwiw I've crossed the pyrenees on a 5-speed city bike on my way from sweden to spain.

Maybe a local bike shop could help you find a decent second hand bike? Good strong wheels and puncture proof tires would be at the top of my list.

Check out the Thorn bikes to get an idea of the different kinds of touring-specific bikes available, and maybe adapt a cheaper bike to be more similar - hope that makes sense :/