I have a Alma BB in Epi and feel even for me alone it can be a pain to open. It's quite stiff and usually requires two hands to open and get into it. I couldn't imagine carding not that bag with a baby in my other arm, but I also do not have kiddos (yet.) and love my BB.
I also have a Reverse Pochette Metis and find wth a baby it could feel a bit heavy but is easy to get in and out of.
Out my my collection (b/c those are what I'm familiar with.) I would say something light and easy with no veshetta: Bloomsbury. Super comfortable to wear, or zips closed and holds more than the BB. It conforms to your body so even if you had the baby on the same hip as your bag it wouldn't be as uncomfortable as day the BB and it has a great exterior pocket for easy access to your phone. I would imagine that will become important when you baby just looks so adorable you must get a photo in that exact moment. [emoji6]
Others I could recommend would be Speedy B 25 (but it sounds like that isn't the bag for you.) Pochette Accessory, a light weight option and also very comfortable and would be easy to toss into your diaper bag if it's too much to carry baby and diaper bag and purse. (My girlfriends mama purse.) and finally the favorite would be my suggestions. Hope this helps and congratulations!!! How wonderful!