I can certainly relate to your problem. I always wear knit paints with elastic waists. The elastic can't be too tight, either. Then sometimes I cut the elastic just at the waistline to expand them a little.(tacky, huh) If I'm not as bloated, I put a safety pin in to make them tighter. Of course, I wear my knit top out and not tucked in so no one knows.
I think the pants with the drawstring are a great answer, also. Maternity pants could do the trick, too. I can't wear hip huggers either....they just aren't comfy on me.