I hope you’re not using an old worn out mattress. Maybe some memory foam to help even out the surface. No headboard? What about a dresser for their clothing?

Is that the designated bed spread to be used? If so your drapes can have blue notes in it. A nice wall painting incorporating some of the colors in the room would work.

It doesn’t look like you have a lot of room for an accent chair and I’m not sure how much room you would have if you put a bench at the end of the bed.

Maybe a tall ficus plant (can be fake) in the corner by the table and mirror.

Add a second nightstand and a power strip for recharging electronics. The colors are nice and relaxing.

I’d do an upholstered headboard. Lots to choose from and very reasonably priced. Patterned window panels. And only one circle item on the wall. You have somewhat of a blank space, have fun.

I think the circular piece (carving?) above the bed would look nice lowered a few inches, and agree with the idea of adding a second nightstand of some sort with a lamp and landing place for a book, glasses, etc. I don't think the radiator needs to match your walls. If anything, I'd paint it your trim color (it looks like it might be a creamier white than the current trim color).

The depression on the mattress looks to me like kitties have temporarily rested there, not necessarily that it's a worn out mattress.

It looks like a pleasant, light filled room.

I would turn the chest of drawers and use it as your second nightstand with another lamp on it. If two lamps will use up all the outlet space on that wall, get a splitter that turns one plug-in into three. To unify the two different nightstands use identical framed rectangular mirrors over them. Or if the room has an ensuite, skip the mirrors.

Choose the rest of the furnishings for comfort:

-a comfy small scale armchair. Navy would be a good choice.

-blackout curtains that can be drawn back or pulled closed to cover the window fully. Again, navy is nice.

-a fluffy knit afghan folded across the end of the bed.

-I'm an allergy sufferer so a box of tissue and small garbage can next to the bed are always appreciated :)

In my guest rooms I have a comfy chair with a reading light behind it. I don't have chests of drawers in one room but I do have one of those folding suitcase stands that you find in hotel rooms. People who are only staying one or two nights usually don't fully unpack and having a stand allows them to live out of their suitcase if they wish. I also have a small bookcase where I keep a few books with ideas about places to visit locally and a few menus from local restaurants for people who won't necessarily be taking all their meals with us. I also keep a notepad and a container with a few pens and pencils in it.

A trash can and place to charge computers, tablets, and phones is really appreciated. I also have printed up some cards that allow us to enter our home wi-fi password and directions for using our keypad locks so people don't have to wake us up if they come in late or leave early.

I would add blackout drapes similar to the wall color.

A pretty throw across the bottom of the bed.

And a soothing piece of art to the right of the window.

A simple wooden arm chair in the corner just to put on shoes would be plenty.