J.H.
I got the Paraguard (copper) IUD when I was nursing my youngest because I didn't want any hormones and I've been happy with it. My periods have been heavier, and typically last a full week now, but it is nice not having to think about it. Also, the copper IUD is supposed to actually last 10 years, versus the Mirena IUD which lasts 5 years.
My sister has the same thing (she got hers before I did) and has had some problems with cramping, but I think her doctor is going to put her on very low dose birth control pills for two months with is supposed to clear that up. But we both are glad we chose this option.