townfield saddlers do hinged stirrups. They look just like the sprenger ones and they're only £19.99 (from memory!) best stirrups I have ever ridden in!
Beware, I had a pair of the cheap ones. Was out hunting at the gallop, off his back, when the rivet holding the hinge gave way, one second up, next second hagning off his side!!!
The theory is great, I had really bad ankles and never any pain with these but would now be a bit wary of cheap versions, it could have been nasty, luckily it wasn't!
I have weak ankles, but found that they do strengthen with plenty of riding exercise. Some stirrups aggravate them more than others, I currently have flexi irons (not sure what make as they came with the tack that came with my horse, the old owner couldn't get on with them) I love my flexi irons and I am much more comfortable in them, although when I tried a pair a few years ago I found them way too wobbly. Not sure if that was down to having a weaker lower leg position then or the irons being different.....
I struggle with safety irons though as I feel my ankle will wobble out the side, and any that have a sloped or curved tread.
I've used the chunky cheese grater ones a couple of times too and quite liked those.
Getting supportive boots will help too, rubber riding boots are useless, I have been much more comfortable in mountain horse boots (I have long ones and short ones) than previous boots (not just rubber ones, cheap generic joddie boots, old fashioned long leather boots and short lace up type boots) I think getting a brand that have thought a bit about support for riding is worthwhile. I like my mountain horse boots and so does DH who also has weak ankles, think ariats would be good too having tried some on but haven't got around to parting with the £££ to buy any yet.
I have an ankle replacement and really struggle however I find the sprenger flexi ones good but are brilliant if you add endurance cages, which I now wouldn't ride without
townfield saddlers do hinged stirrups. They look just like the sprenger ones and they're only £19.99 (from memory!) best stirrups I have ever ridden in!
deffo get sprengers if you can - you can usually find some seconbhan on eBay if the price scares you.
I got a pair of rhinegold flexi stirrups for £30 and they do the same job as the sprengers although I do find the sprengers slightly better
I have some black ones by Compositi that have springs under the treads to act as a suspension system - the treads are slightly wider too which really support your foot. They were around £25 quid about 4 years ago.
I once found half of a flexi stirrup in the grass verge which put me off them for life...!
This is off the subject a bit, but I broke my right ankle twice and then ripped the ligaments as a 3rd injury over a period of 3 years - all horse related !
I find using a good, ideally, made to measure pair of leather hunting boots to ride in all the time helps. Far better support than jodi boots/chaps or muck boots/chaps for everyday riding. Maybe good boots and specialist irons will help you.
I have had Sprenger stirrups years and highly recommend them. I get terrible pains in my knees and ankles after about an hours riding and as I regularly go on safari holidays (sometimes 8/9 hours in the saddle a day) needed something that would keep me in reasonable shape for the trip. You can get cheaper versions which mirror the articulation points of the Sprengers and to be honest I hear they work just as well - my friend has a pair and uses them on our sarafi holidays too - I thinks that they are around £20 - 25. Good luck!