I've lost a lot of hair after having DS2 (brunette, straight), and cut it in half to just above my shoulders with a long layer & slight shaping around the face. Any real layering would just lose what little body my hair has.
To be honest, I just went with the hairdressers recommendation.
Have you been to your GP? I went, and they ran some basic blood tests, checking thyroid, iron etc. There may be an underlying (and treatable) reason for the continued loss. Do you know if you are losing it from the root, or if your hair it brittle/fragile and breaking? It may be useful to tell the doc.
Some loss after having a baby is normal, but it can be so disheartening. My tests were normal-ish, but my iron levels were at the very low end of normal, so I've started taking a supplement. I've also started taking a multivitamin, just in case it helps. I had the same thinning after DS1 too (both bf), and it did grow back again eventually, so I'm focusing on that!
Definitely recommend Gp. It won't hurt to take an iron supplement anyway. I've always had thin hair but lose it due to stress. I try tokeep mine in a slightly inverted bob which gives the illusion of thickness. Also no conditioner as it weighs my hair down.