Portable Aircon unit for garden office

They don't need servicing as such. They are sealed units that don't need to be refilled. They just keep working until they don't anymore. The only servicing you need to do is to clean the filters every so often and empty the condenser tank at the end of each day if you aren't going to plumb it in to continuous drainage.

You need to be a little careful though. These units can be quite noisy. If you're going to be doing calls or video meetings for example the background noise from this might be very intrusive, since the compressor motor is inside, rather than the external setup you would have with a split system.

My advice would be to get an air conditioner that's at least 7000 BTU's, if not more. 9-12k would be preferable since you're going to be south facing. A weaker machine would be running continuously to just pull the temperature down a few degrees. Something more powerful would be able to quickly drop the temperature down and maintain it while clicking on and off in the background as it needs to.

Just in case you aren't already aware, you need to vent these air conditioners outside just like you do with tumble driers and their heat exhaust pipes. Make sure you are willing to either cut a hole through the wall to do this, or get a window seal kit to put the pipe through a window and seal the rest of the opening to prevent too much cold air being wasted out the window (or outside hot air from getting straight back in)

Finally, do you happen to have an Argos Clearance Baragins store near you? These are by far the cheapest way to get an air conditioning unit, and between now and about Easter time, you'll see lots of them popping up at lower prices before they start to shoot up with demand.

If it is a properly built garden room and not a shed (you imply bifold doors so assume double glazing etc) then get a proper split unit. A 2.5kw split would be perfect.
I have this one Panasonic Air Con Etherea CS-Z25XKEW White Wall Mount Heat Pump R32 A 2 5Kw/9000Btu Install Kit (orionairsales.co.uk)

Much more efficient than a portable aircon and whisper quiet - If you have it on Auto fan, once the room is cool you barely hear it. We have it in a south facing room with an all glass front and it uses around 2kwh or less per day (a portable would be around 1kwh per hour). Added bonus of being able to use it as heating in the winter too.

I'd first look at reflective solar film on those doors, the film goes on the inner side and can cut sun heat through glass by 40%. This sort of film is what's used on glass conservatory roofs to cut the temperature by 10° C. Done professionally the film is pretty neat and can also add a bit of extra privacy. The fitters get very busy every summer so plan ahead. Next I'd look at ventilation, add windows to give a through draft. Aircon would be quite expensive to run and works best when all windows are closed, you'd only want to use it for a few weeks per year.

Reflective Film, and the Mini-split option get a Vote up from me. 7-8hrs a day, deserves a bit more investment into the room.

How was your install?

How much did it cost you all in?