The recommendation above to add rather than replace might be a very good choice. If you will forgive me both mixing and mangling metaphors, a commuter with only one bike is like a Jedi who bought his lightsaber on craigslist.

If it were me I’d at least consider the following: get the fit issues worked out (if possible) and turn the KHS into a solid commuter bike with racks and fenders. Then get a decent road bike, such as maybe that Trek 1500. It will definitely be faster and more fun, if a bit less practical for grocery runs in the rain.