Ok, if I see this correct, you want the "Really amazingly fast recovery" part of Mystic Recovery, without the rest of the power, and it should work when you are engulfing yourself in fire as a part of healing yourself after a fight, not during a fight.
Then let's just do that. Let's take "Really amazingly fast recovery" as a -4 power. It allows you to enter every fight without any physical consequences, but you can't heal yourself during a fight, so I think it is priced fair like that. Now to the discounts. For an amulet, which is probably the best form for an item like that it would be +1. Human form to represent the fact that you need fire to activate it is another +1. Since you want it to heal everything, there will be no catch, which is +0. You can still be killed, but it has to be done in one conflict, or your enemy has to make sure you can't immolate yourself. This would be a -2 total, which is still pretty great for the benefit.
The holy catch would still apply of course (along with the discount), but you would be able to heal yourself from it with the phoenix power. It makes sense, since the phoenix doesn't really have anything to do with holy stuff.