The problem with heel blisters is that there can be several different causes to them. Typically the heel pocket is either too big or too small or the ankle & forefoot aren't being held down well enough to prevent the lift. If you can find a good bootfitter, they can help you. Look for reputable ski shops, hiking shops or specialty shoe stores, even if they don't carry the brand you want, they can often fit your foot and give you some pointers on what to look for specific to your foot.
Typically stiff boots are utilized in soft conditions or with only a portion of the boot engaged at anyone time, so the flat sole doesn't cause problems. But if you are on hard ground, packed trails or roads, then even with a perfect fitting boot, you may not be able to make them work. One solution is a rockered sole, this will make a stiff boot + hard ground much more doable.
Compeed is an amazing product to prevent blisters or deal with them once you have them.
Typically stiff boots are utilized in soft conditions or with only a portion of the boot engaged at anyone time, so the flat sole doesn't cause problems. But if you are on hard ground, packed trails or roads, then even with a perfect fitting boot, you may not be able to make them work. One solution is a rockered sole, this will make a stiff boot + hard ground much more doable.
Compeed is an amazing product to prevent blisters or deal with them once you have them.