Non hormonal IUD

I am 3wks PP and I have been trying to choose a type of BC. After my first I went on the mini pill and gained all my 25lbs of baby weight back. Even though I was eating healthy and exercising. And could not drop the weight after It came back. So decided I want to try the IUD this time.  But I am paranoid about weight gain. I don't want to go through that again. And we aren't planning on trying for #3 for 3-4yrs. Anyone have positive or really negative reviews being on a non hormonal IUD?