Sorry to hear you are suffering.
I was first diagnosed with peroneal tendonitis in both feet about 10 years ago by MSK podiatrist at local hospital (was already seeing podiatrist for other MSK issues so was able to get early diagnosis and treatment fortunately). The podiatrist changed my orthotic prescription and added postings (wedges of material underneath orthotic - think that's what they're called) to offload weight from the tendons and I was told to wear my orthotics at all times. Also had some exercises to do and wore a night splint most nights which helped with morning pain.
This worked well and the tendonitis improved to a point of me not being aware of it very often.
Then a combination of installing hard flooring in the house, lapsing back to wearing slippers/sandals while WFH during lockdown brought it back and this time I developed pain in my ankles as well as my feet.
Went to private MSK podiatrist who confirmed original diagnosis and gave me new orthotics with increased postings/wedges underneath to wear to wear all the time. Also tried taping - helped with pain but gave me huge skin irritation after a while, some kind of laser treatment (no benefit) and exercises. Podiatrist then recommended I see physio for tendon massage/manipulation as I still had pain.
Physio worked on tendons and tight calf muscles and also advised wearing of orthotics at all times. In my case poor biomechanics (back, hips, knees, feet etc) are the cause of my peroneal tendonitis and I am still working with the physio to improve things and resolve a host of longstanding issues.
My tendonitis is currently well controlled (minimal pain & stiffness). I wear my orthotics all the time apart from when I'm in the shower or asleep - I have indoor trainers that I put the orthotics in for around the house. I put them on first thing in the morning and take them off last thing at night when I go to bed. I do leg and foot stretches everyday as well as a whole lot of other physio exercises. I see the physio regularly and the podiatrist when I need an orthotic adjustment. I also wear night splints from time-to-time when I feel the need.
Has your physio suggested you see a podiatrist for customised orthotics? With regard to the best trainers I buy neutral running shoes (New Balance, ASICS) as they tend to fit me well and have removeable inner soles which I replace with my own orthotics. I've been advised that orthotics should not be worn with memory foam and I'm the first to admit that orthotics are quite limiting in terms of what footwear you can wear - I only own "sensible" footwear these days!
I hope you feel better soon.