It’s not the best idea to put paper/canvas art of any value (sentimental/monetary) in a bathroom. The humid conditions are not favorable.

Also, art is personal. Why would you want someone else to choose your art.

You could take a picture - or find an image that you like - and have it made into a poster or a tapestry.

Also - tapestries, prints, etc., are available at Etsy.com

https://www.etsy.com/listing/1513410631/textile-vintage-floral-tapestry?gpla=1&gao=1&dd_referrer=https%3A%2F%2Fwww.google.com

Hard to comment without knowing the size or layout of the room. I'd wait until it is built to see what you actually need. The wallpaper has so much movement and visual interest. Maybe you don't need art or as much of it as you anticipate?

Look for something you love and do not worry about it matching the paper. Art is very personal. Look for something that has the greens in it but that is about it. You can visit some local galleries in your area to buy original local artists works rather then prints online that will most often cost the same. I can also see some very nice watercolour botanicals going very nicely with this paper or a very large floral study-close up of a single flower.

How about something like this

I'd select art with extremely large matte to form a barrier from the patterned wallpaper

If you need a mirror, I like this wavy frame style for that wallpaper.

Suggest waiting until bathroom is finished and papered. You’ll have a better sense of size (maybe two smaller prints would work better) and the frame has an influence also. In the meantime, look for inspiration. Your combination is lovely and I’d aim for a soft, classic feel. Try Etsy as they have more unique selections and usually carry sizes options.

https://www.etsy.com/ca/listing/1842110692/antique-english-cottage-printable-art?epik=dj0yJnU9ZkhSUk5veklyTzdfS19DWXUyRHd5d2Zya2ZJOUgydkImcD0wJm49aXQ1cUZ1WE5uemdxVTJYVmtaUEc3USZ0PUFBQUFBR2h0VmhZ