When I am making the pattern I try to include several "darts" to tuck in excess material and also provide a rib structure. I've not had an issue yet with heavier things buckling the form. A steamer is the recommended tool for shrinking, and take your time to really get it down to its minimum dimension. The material can buckle when removing your form, and that does create a weak spot, but it can be resteamed to firm it up - just be cautious so you don't lose your shape. Photos would definitely help!