Dog carriers are awful. Timbuk2's Muttmover will fix that for you, assuming your dog actually fits. Now in multiple sizes and colors.
The Muttmover is packed with thoughtful features to facilitate the process of packing it with your dog (or cat). Airmesh and padded straps are essentials here, along with an optional sternum strap and enough storage for all the things you need to carry that aren’t dogs.
The Muttmover can open mostly flat, is fully ventilated on both sides, and has head holes for your pup on either side that can be zipped closed, along with a waterproof liner for obvious reasons.
Timbuk2 rates the bag suitable for up to 20 lb dogs, and I can unfortunately say my 21 lb dog didn’t fit, but if yours does, this is by far the least painful way to carry them.