I have had a tender Achilles tendon (tendonitis) for several years, mostly in my left heel. Normal boots tend to aggravate it as the top of the boot is level with the tendon and bangs it with every step so I was only doing the laces up low down which meant I received little support from the boot. This a bit of a problem when you make your living by walking and photographing the hills and mountains around the world.
I noticed that my ski boots and the winter mountaineering boots that I also used for snowshoeing don't cause any tenderness. They are much taller boots than normal hiking boots. My last pair of boots were Meindl Borneo's and they were better than some boots I have had but still not that good as I couldn't do them up very far.
A Google search for 'walking boots for Achilles tendon' threw up a few options, one of which was a much taller hiking boot called the Meindl Dovre Extreme. These are only available in the UK through hunting, shooting and fishing outlets not the normal outdoor gear shops. Fortunately, we have one in Bakewell (Brocklehursts) that stocks Meindl, just a half hour drive away. They stocked a couple of different versions but the Meindl Dovre Extremes were the best fit to my feet.
I have had them for almost 6 months now and walked several hundred miles in them. They are about 4 inches (10cm) taller than my old Borneo's, lined with Gore-Tex so completely waterproof (good for wading into rivers to get close to waterfalls for photos) and very comfortable.
I thought the extra height may be a problem but it isn't, I don't notice it. The boots are so tall I also don't need to tie the laces tight, the boot shape keeps my foot in place. I don't go over on my ankle at all any more and there is no longer any tenderness of my Achilles during or after a walk/hike. The only disadvantage is the price, they are bloody expensive!
If you have a similar problem with your Achilles it may be worth your while trying to find some of these, or something similar, to allow you to continue walking the hills.