It's a compromise but I'd probably go with a frame bag and a holster that's designed for a purse or back pack. It can be unzipped partially and the gun is ready to be drawn. It also attaches with velcro loops so it can be installed/removed without exposing the gun if you're in a public area.
https://smile.amazon.com/Aduro-Bicyc...me+bag+cycling
https://www.crossbreedholsters.com/p...fender-pd.html