I had Great Danes for many years. All giant and very large dog breeds, must be kept on some kind of soft bedding, or they will get horrid things on their elbows, which can turn into worse problems.
Many dogs don't like anything which doesn't feel secure. ie. wobbles. I discovered that those big moving pads, such as movers cover furniture with, when moving large pieces. Folded in half or four, they make nice soft bedding for most breeds. While they cannot fit in a washing machine, they are easily hosed down and dried, hanging over a fence.You can also purchase egg-carton type foam padding, to place under the blankets, if your dog is not a chewer.
These things always worked well for me and I never had any dog suffering from hygromas.
There again, a Great Dane and similar sized dogs, mostly do well on an old sofa or love seat. My friend in England, from whom I purchased my first GDs, many years ago, had a room in her house, just for them. All around the room were old sofas and each dog had his own. Worked well for her.
Lizzie