Also have a dual purpose room. We did inexpensive white shelving units around two walls, with fabric boxes to stash stuff, (office, and my "crafty" supplies), threw in a few decorative items. Got a tall basket for rolled up mats/foam roller storage, a complementary lower basket to throw in the requisite elastic bands, small hand weights, etc. Decorated walls with pics from our travels, framed with colored mats.

Placing the desk along one wall allows more open areas for the gym and related activities.

Hi Katie, can you move your office somewhere else while your guests are staying? Maybe put the bedhead under the window and push it hard against the left hand wall, that will give you about 67cm between the bed and the door, room to sneak in a small bedside table (if queen bed is 153cm wide and room is 220). Not ideal as the person closest to the wall would have to shuffle down off the end of the bed but it's a very tight space for a queen size bed. You could maybe then put a small chair or two and table against the wall between the end of the bed and the wardrobe for a sitting area for your guests. if your desk needs to stay would it fit along the wall where the bed head is currently? Assuming you don't want to swap the bed out to a double.

An instagram style wall - small white square picture frames hung evenly in rows from height of computer screens upwards, with some of your favourite candid pictures. would look good all printed in b&w, or sepia to tie in with your colour scheme...or alternatively go bright and vivid! summer beach shots, pets, kids, holidays etc