M.R.
It would be worth trying Mirena again. Go to experienced fitter and there should be no problems with insertion. General problems are irregular bleeding over 6-12months after insertion, the body can expel the IUCD (this is the same with any IUCD), rarely although it can happen the uterus is perforated at insertion and the coil may be elsewhere. This is not harmful although may be painful and would need an operation to remove(again same with any coil) but generally well tolerated and very effective.
M.