You have a high rigid arch as it is called. That in combination with a narrow foot explains your heel slip. You will probably be OK if finding a shoe on the narrow side with proper length. My foot is hotdog shaped...long and narrow and so I can't ride a wide shoe either. Where our feet however are dramatically different is I have a medium to low flexible arch. If my foot isn't supported with a suitable footbed, my foot extends in length when pressured requiring a longer shoe. I find Specialized shoes to fit like Nike sneakers...on the narrowish side...so they maybe the ticket for you. But what you need then...Specialized sells 3 different footbeds...is the high arch foot bed. I believe if you get good support under your high arch, your heel slip issue will disappear.
Hope that helps.