Watch how your dog actually sleeps first
Spend a few evenings noting your dog's favourite sleeping posture before you buy anything, because that posture decides the bed shape more than breed or size charts do. A side sleeper who flops over with all four legs extended needs uninterrupted flat space. A dog who tucks his nose toward his tail and rounds his back is looking for contact and containment. A dog who wedges himself under cushions, blankets, or the edge of your duvet is asking for cover, not just padding. Many dogs rotate between two postures, so note which one he chooses for his longest, deepest sleep rather than a brief daytime doze.
Match the shape to the posture
For the sprawler, choose a flat mattress-style bed with no raised edges eating into his stretching room, long enough that his head and hind paws stay on the surface when he is fully extended. For the curler, a round or oval bed with a soft bolster rim gives him something warm to press his back against, and the rim doubles as a chin rest when he wants to watch the room. For the burrower, look for a cave or hooded style, or pair a plain flat bed with a light blanket he is allowed to rearrange, because a burrower given only an open mattress will often abandon it for the laundry pile. Back sleepers who roll belly-up usually accept any flat, breathable surface and care more about a cool spot than about shape.
Size, support, and the dogs who need more
Measure your dog from nose to tail base while he is asleep in his main posture, then pick a bed whose inner sleeping area is longer than that measurement, since a dog who has to hang his head off the edge is telling you the bed is too small. Puppies can grow into a mid-sized bed with a washable cover, but senior dogs and dogs with stiff joints need firmer, supportive foam that does not let their elbows and hips sink through to the floor, plus a low edge they can step over without jumping. Heavy dogs compress thin padding within weeks, so press your own hand firmly into display beds: if you can feel the floor through the filling, your dog will too.
Placement, covers, and the trial period
Put the new bed where your dog already chooses to sleep, at least at first, away from draughts, radiators, and busy doorways, because a perfect bed in the wrong corner loses to a mediocre spot he trusts. A removable, machine-washable cover matters more than decorative fabric, since muddy paws, shedding, and the occasional upset stomach are certainties. Give him several nights to accept it, and resist moving it around daily. If he consistently leaves it to sleep pressed against furniture, add the missing element, usually a bolster or a blanket, rather than replacing the whole bed. Once you know the shape, size, and corner he has settled on, share this dog's profile with relatives you pick through KinsLe Family Sharing; those family members can then open the profile of the sprawler, curler or burrower who chose that bed.