Lax abdominal rectus muscles? Do I need a girdle?

[Adreamz]

I'm postpartum 7 days. I still have a bump like I'm 30 weeks pregnant (it's lovely and neat) but when I had my first it was more like a flabby belly.
Midwife said my abdominal rectus/obliques are lax. Trying to see if there is anything I can do to help as its getting me down. Read something about girdle, I'm happy to pay the money if they work, but wondered if anyone had any advise? Also if you have used one which make did you go for?

The physio I saw for SPD suggested wearing spanx post birth for this as my muscles had separated a lot. She recommended the cheap primark version in fact. I've worn them a little but felt that the tightness of them was uncomfortable 'down below' especially the furst few weeks, with stitches...