touring bike sounds perfect, and maybe a used 'sports' road bike - essentially a bargain tourer, which may be better for commuting than a 'real' dedicated tourer. If you'd be locking up on the street at all I'd definitely go with the sports bike - will have much of the same geometry, pannier eyelets, etc. without the expense.

My mid 80s trek 500 with sports geometery has a nice smooth ride and a good gear range. I prefer that to a Bianchi hybrid I bought new in the 90s for longer commutes, touring etc. Lighter quicker and lower uppper body to cut wind drag. The bianchi had a lower granny (triple crank) but no contest in which was faster or more fun to ride......

You could also go with a rigid mtb (1" slicks) or a hybrid for stability but a tourer or road bike would be nicer over that distance!