Start with the space your dog uses when resting, then compare the selected bed's overall footprint and usable sleeping area. Raised sides and bolsters can make those two measurements different.
For a product-specific comparison, Snooza's Orthopaedic Dream Sofa information lists an orthopaedic foam base and raised bolsters. Buddy & Belle's Small/Medium Orthopaedic Lounge lists a memory-foam mattress, an open front and a removable cover. These are features of those models, not a construction shared by every dog bed.
Check the model's foam or fill description, entry height, base and intended location. A calming or orthopaedic name does not establish treatment for anxiety, arthritis, hip dysplasia or recovery from surgery. Ask your vet about an individual pain or mobility concern rather than choosing from a category-wide therapeutic promise.
Check which parts are removable and which can be washed. Follow the directions for the particular cover and inner material instead of applying one weekly cleaning schedule or assuming every cushion is machine washable.
How do I compare sizes?
Compare the usable resting space as well as the outside measurements. Use the actual model's sizing information rather than adding a universal number of centimetres.
Does every orthopaedic bed use memory foam?
Check the listed material. The Snooza and Buddy & Belle examples have their own foam descriptions; the category name alone does not establish an identical construction.
How should I choose for outdoor use?
Check the selected model's intended location and stated fabric properties. An outdoor style name is not a blanket waterproof or cooling guarantee.