I found what I feel is an ideal solution:
Osprey Stratos 24 Backpack
Put one of your shoulder bags in it for the lenses and camera, which will still leave room for a couple of water bottles, a light rain jacket, a few essential bike tools, extra socks, snacks etc. That's what I've been using for my day- hikes and I barely know it's there.
The Stratos is great for staying cool since it doesn't lay flat to your back, leaving space for airflow and the waist strap in combo with the other adjustment straps keeps the weight on the hips and off the shoulders. When the baby comes it will hold a bit of baby gear too (perhaps at the expense of some of the camera stuff but that's family life
)
I've tried a couple of dedicated camera backpacks but they're are not nearly as comfortable on a full day out and about, nor as adaptable to the other stuff you want to carry besides photo gear.
Watch for sale prices as I bought mine for under $90 a few weeks ago. Regular pricing seems to be closer to $120. It's a really good backpack that serves multiple purposes.