I want to buy a comfortable pet bed. Any suggestions from experienced pet owners?
In my experience, some dogs are pretty chill and will sleep on anything while others are super picky.
I had a border collie and he used a bed similar to this one for years. I think I spent like $30 buck on it.
I also used to have a chow and she unfortunately didn’t like any of the beds we got her and chose to sleep on the floor.
You can also try talking with your vet and seeing what suggestions they come up with. 
Depends on their sleeping style. If yours is a curler and curls up then a round bed. If yours is a side sleeper and likes to stretch legs you need something more rectangular. If you have a burrowing breed or a descendent of one-- you need a hooded “cat bed” styled one. If you live in a hot area those trampoline beds may be better. Honestly it all depends on your dog.
My dogs bed is about 6 feet x 3 feet, costs a few hundred bucks, and fits a couple adult humans when he’s not in it 
and how big is your dog? just to know the proportions
Same 
We now have 3 of those size beds - one for each cat - in the hope some humans can get a good nights sleep.
Just to be clear - its a couch, my dog sleeps on the couch. He’s a medium sized dog, about 40lbs I think. He likes to curl up when he sits or sleeps, so we can all fit on there.