Equine arthritis & joint supplements UK...?

So my beloved 22yo Fell x has just been diagnosed with probable arthritis in one hind foot, just above the coronary band (so that's small pastern joint?). She hasn't been lame but has been a bit sluggish and developed a bubble of fluid there, hence calling out the vet. She's been put on bute for a week and no riding for a month, then back into light work slowly. She already gets a Glucosamine-MSM-boswellia supplement, plus a NAF general supplement and magnesium to guard against laminitis. Any thoughts on these supplements? Should I be changing/adding something? Please only suggest things I can get in the UK. Thanks!