I'll admit to being lazy and cheap. I also have the support problem. Now that I'm fat I'm a 38 D or even a 38 D.5!
Actually, I'm more cheap than lazy. While I can bring myself to spend $30 or even $40 on a pretty bra, I cannot bring myself to spend $16 on the matching undies. TMI alert - what if Aunt Flo visits early and ruins them!
I solve this problem by limiting myself to white, nude and black and buying color coordinating panties at Express or even Wal Mart They have new "fancy" nylon Hanes biknis at 2 for $6!!! I'm currently testing them. If they last a reasonable amount of time I'm stocking up.
As for the problem with wearing a bra several; days per week while wearing the undies only once a week (obviously!), the practical - yet expensive solution is to buy one bra and several pairs of matching panties. That way you can wear the fuschia lace set 3 times/week.