Hi RA,
Disclaimer
I'm no doc', just telling you what help me.
I feel your pain - literally. I too have what I can only describe as "weak" ankles. This is from decades of playing squash, and countless instances of rolling my ankles. I too wear orthotics, My feet are also wide, though not as wide as yours. Unsurprisingly my "ground feel" is poor also. This was once explained to me as a a breakdown in the biofeedback loop from my ankles, as a result of injury over the years. It can be repaired somewhat via rehab, but not completely. Unfortunately, despite multiple rounds of rehab, my ankles are still progressively getting worse, and I'm starting to look into surgery as an option.
This was all bought to a head a couple months ago, when, on the way back from Mt Cloudmaker (Kanangra-Boyd NP) the trail crumbled beneath me, the edge of my boot dug in after dropping 30cm, and I rolled my ankle, with the full weight of a heavy pack (was trying out some new winter gear) and me on my ankle, over I went for a roll down Mt Berry. It took me 5 hours to hike out to my car, with 2 more significant falls. Climbing up Smiths Pass was tough.
During and before this trip I was using a pair of Keens boots, very wide, decent "ankle protection", with a very stiff sole, and gaiters. After my injury I did a lot of read about the false sense of "ankle support" boots provide.I have since moved to a velcro strapping system I purchased from the local chemist from Thermoskin.
Thermoskin SPORT ANKLE BRACE -
http://www.thermoskin.com/products/view/sport-ankle-brace/I have been using one for the past 2 months and it has saved me a number of times, because effectively your ankle is strapped. The support ids far superior to any boot I have worn. I intend to add a second one to my kit for the other ankle, and add gaiters to top it all off. Lastly, I also intend to add pair of walking poles to my arsenal to improve my stability.
I have discarded the Keens boots in preference for Vibrim soled trail runners, for enhanced feel and grip. I settled on the New Balance Leadville V3, due to the very wide fit. I am using a D width with the ankle brace on and they are snug but comfortable. I normally need a 2E, so they are wide! I recall there is also a 2E width available, but apparently the only place you will get them is a New Balance store, Athletes Foot can't get them. The New Balance site doesn't list a 2E option for Australia.
New Balance Leadville V3 -
http://www.newbalance.com.au/pd/leadville-v3/MTLEAD-V3.html?dwvar_MTLEAD-V3_color=Black_with_Orange#color=Black_with_Orange&size=11&width=DThe next thing we have in common is back pain, I spent 8-12 weeks on and off between Jan - April with significant back pain, enough to keep me out of work for a couple weeks at a time. Any amount of walking, standing and sitting caused lower back pain, extending into my left hip and down my left leg. This was initially diagnosed as sciatica. I went for cat scans, X-rays, was given pain killers and anti-inflammatory meds. The only real relief I got was from laying down. Was so bad I ended up on pain killers. Physio would sort me out for 1-2 weeks then the pain would creep back in. I ended up with a pretty unhealthy codeine habit.
The solution for me was stretching and a foam roller. Every morning I spend 30min stretching hamstrings, calves, quads, groin, back and ITB. My focus being hammies > quads > ITB > groin > back. I then use the foam roller on quads, and back. After about 1 week of this, the pain lessened, 2 weeks it was mostly gone, 3 weeks it was barely noticeable. If I stop this routine the pain level creeps up again.
Anyway I hope the above is useful.
TLDR - Try trail runners and an ankle brace, with walking poles. Stretch lots.