The GST would be more comfortable on your shoulder, but it is heavier compared to the Neverfull. Don't really care for the Saleya ~ I'd pick the Neverfull over the Saleya. Have you looked at the Cabas?
The GST is a beautiful bag & the price will be going up fairly soon, so if you are thinking that you may eventually want a GST consider getting it now. I hear the increase is just as much if not more than an LV. The LV choices won't break your pocketbook, so maybe you can pick one of those to rotate at a not-so-later date???
As a new mom, your arms & body are going to get a workout for the next few years. If added weight or maintenance is an issue, I would for sure consider the Neverfull as the bag to get since the GST is a little heavier (leather -vs- treated canvas.)
CONGRATS to you as a new mom!