looseness anywhere in the boot will cause skiers to compensate with whatever you can throw at the ski edge. meaning that good skiers inherently know what they want the edge of the ski to do on the snow, and when there is even subtle movement in the command center (ski boot) you compensate either in use of micro muscles and or body movements to make it work. in your case it shows up in your feet and ankles. to solve this conundrum, you have to get to the source of the problem. ankle pain is the symptom, somewhere else in your set-up is the actual cause of the compensatory action.
you are making the same mistake again. the target fit, size and shape of the hero 97 will not be that different than the redster in the 97 last. a better thing for you overall will be the rossi hero zj+. this boot is sold in europe specifically to ski instructors and high performance skiers. in the u.s. it is only referenced in the race catalogue for rossi/lange. you cannot always buy your way into boot fit nirvana, sometimes you have to sneak up and surprise a good fit...or find a guy that gets you and your foot and has the skills to manipulate your boot to work for your individual set of circumstances. marginal talent boot fitter + with bad boot choice = spin cycle!!!
a liner may help... either zips or a foam injected, however the holding power of a performance boot should come from the shell not the liner. plug boots all have very thin but firm liners that contain the foot well when in a low volume shell. a proper performance fit is achieved when you are able to drive the foot down and back into the shell for control.
the issue with containment of the rear foot with a low volume instep heel or ankle is that for the measured length of any shell the instep height will be somewhat relative. what this means is that to get the shell down on the foot you have to get into a shorter shell that by design will have a lower roof and a narrower heel shape. zj+ in a 23 with the toe box extended and any fit work for boney spots ground to match your foot...otherwise you are headed down the same road with a 97mm "pro" last.
the x factor for you also will come down to a proper assessment of your foot to see if there is something going on with the mechanics of your foot that is also leading to your pain.specifically i would like to know if there is some hyper mobility in the ankle, midfoot, or 1st and 5th metatarsals joints :(
good luck sussing this out, look out for boot fitters with rainbow unicorn horns and pixie dust :)