I was wanting to incorporate medicine ball throws into my program, but can't figure out which poundage to go with. I have just a regular 12lb ball, but that's easy. It's not like i can walk into your local sporting good store and find a 25lb ball, which is probably what i'll try, but not sure what poundage to start with. I don't want to purchase one online and find out it's too light. Any suggestions on poundage?