I was like you few years ago when I had my 1st baby. I chose the Neverfull MM as it fits just enough but I wish I had gone with the Mono instead of the DE as it took me two years of constant use for the leather to soften a little.
Considering you already owned the classic speedy, it is okay to keep them away as they wouldnt be too helpful if you are carrying the baby. Even with the bandouliere strap, it will be a hassle to zip and unzip, and the leather strap may be uncomfortable if you fill the bag to the brim. Another alternative of totes would be the Goyard Artois or Longchamp Le Pliage tote that comes with a zip, if you wanted more security. The Neverfull in MM size is not too big, in my opinion, but has taller sides that allow you to put any consultation documents when going to the clinic and put a midsize thermos, milk bottles, napkin, wet wipes, facial tissue, barrier cream, etc.
The Speedy B in 25 does not fit as much with smaller opening, but once your little angel starts eating solid food (and running!), you can invest on the Speedy B. In fact, u can still use your classic speedy if you have one toddler (walking and running). If you will add more family members, a good tote is going to help as you could also pack lunch items/meals when you are out and about with your kids.
Here is wishing you a happy pregnancy and a safe delivery!