If this is your first camera bag, I highly recommend a small camera bag that can also act as an 'insert'.
I have the Think Tank Mirrorless Mover 20 and it's been great for this purpose - great size, nicely built, has a rain cover, and well priced. They also make smaller and bigger sizes depending on how much you need to fit.
This allows you to have a very versatile set up. You can use the bag as a standalone bag when you're out shooting, but when you're traveling or hiking, you can just pop it into your normal bag and be able to carry all your other stuff with you (water bottles etc.) and your camera equipment will be well protected.
IMO, this is the perfect place to start and highlights the true benefit of having a small mirrorless system, then you can move on to dedicated camera bags as you see the need for it from there.
In terms of brands, generally look out for Think Tank, Kata, Ona, Billingham, and F-Stop.
Hope that helps.