i wouldnt say they are supportive enough either, the nurses only said sports bra or macom, because they are so supportive. i think the maternity ones are more for comfort, and ease of breast feeding (i found them comfy when my boobs swelled in pregnancy, but they couldnt support me)
im pre-op as well, mine is monday, but i have just bought cheap sports bras, but good ones (i got them in the sales) as i domt fancy spending so much on a macom to never wear it again (plus i would need 2 for washing etc… and thats just silly priced really) xx