Things look clearer now. If you got in well with Femseven in theory you should have no problem with the Mirena coil because both contain levonorgestrel. Evorel conti contains norethisterone which is not the best tolerated progesterone in the world but you obviously got on OK with that too.
This would suggest it's the Oestrogel that's setting off the migraine auras which, incidentally, are caused by cortical spreading depression. There's also a chance the coil is pumping out too much progesterone because it's only just been inserted. I would go back to the patches and if things improve, that means it's the Oestrogel causing problems but if you have no improvement, it would suggest the coil is pumping out too much progesterone - there's chart you can locate online that tells you how much progesterone the Mirena pumps out year on year and it reduces quite a lot over a 5 year period. So if it's the Mirena coil causing the auras, that could stop once it starts reducing the dose.
From what you have said it would seem we suffer from different types of migraine aura. Mine are brainstem auras that are caused by low oestrogen, high progesterone and all types of hormones instability. That's why I've had to manipulate my hormones into a stable condition which means never allowing oestrogen to get too low, not overdosing on progesterone and not having bleed breaks.
Progesterone can be very destabilising so I can't use norethisterone and Utrogestan is very unstable so that's completely out. I got on fine with the Mirena coil pre menopause but the proverbial really hit the fan once I stopped producing my own hormones (which protected me from migraines) and the silent migraines started when I was 43. My migraine sub type starts at menopause and never improves without hormone therapy so I'm on HRT for life.
By the way the Mirena coil can cause thrush type vaginal irritation. I was constantly having infections and vaginitis which was showing up on smear tests.
I hope that helps.
PS I think you will need something like a 75 or100mcg patch with the coil.