Hi OP, I feel you on the clothes front. I was/am quite fashionable and into clothes. I e had more than one melt down because I can't wear what I'd used to (due to BF or quite frankly my new/current size) and felt like a shadow of myself.
I've bought nice pretty bras from Hot Milk (about £35), some Spanx to give me my shape back without the wobbles when I'm wearing tight things, I bought jeans in a size up so I was comfortable that fit well. For me it was worth the money to get good fitting jeans (despite the cost and the fact I'd gone up sizes more than I'd care to admit)
Again as many have said, I wear button down shirts or dresses, or wrap dresses a lot, or stick a cheapo cami under my top/jumper etc so I have easy access. I've also bought some nice bits from seraphine which aren't dowdy. And some feeding too basics fromH&M like vest tops or long sleeved tops with double layers. Good morning quality and cheap.
Whilst yeah right now I can't wear my high necked body con dresses, I still (in my opinion) look nice, well put together and not "dowdy" at all. I make sure I wear nice shoes/heels and always do my hair and make up (if going out, cba with that crap if I'm staying in - it's joggers slippers and mum bun all the way).
Might be vain, but that all makes me feel like me.
My go to outfits;
Wrap or button down midi dress with trainers for casual or heels for out for meals etc
Jeans and linen shirt (joules), normal shirt or T-shirt and jeans/boots
Midi skirt and vest top/T-shirt and trainers or heeled sandals
And sadly recently despite it being effing August: Jeans and a god damn jumper (with a v light cami underneath), trainers or boots.
HOWEVER - if you want to stop BF go for it, some great options available to you including as you know expressing, FF or combo. Doesn't matter what anyone else thinks, your body, your baby, and fed is best. Happy mum equals happy baby. And if you would be happier in your old clothes to feel like you, then that's fine!