They say to drain the coolant because it will be less messy but i've done this 3 times already and it's not worth draining and wasting 2-4+ litres of coolant unless you want to change it. By removing the thermostat without draining radiator you might lose 1-2 litres.
It's not much work imo, don't have to bend or stress that much, if you have a drain pan try put it under the car, you might have to jack it up a tiny bit or put a wood plank and drive over it so you can get some height.
After you put drainpan on floor, remove the big (upper) radiator hose, some coolant will come out, after that remove the 2 bolts that hold the thermostat in and again coolant will pour out, then there is 1 small hose which has a clamp on it, after removing the clamp off that tiny hose the hose might be stubborn to come off, so spray wd40 on the end and keep wiggling, turning it and it will come off, then you have to swap the the temperature sensors over which has a nut on, forgot what size but I used a combination spanner and took it off that way.
Then just refit, take the coolant expansion cap off, put heater on, fan 2 with recirc on and start the car, let it idle for 20ish mins and rev it a little bit once in a while, this is to bleed the cooling system.
When you try starting the car after refitting everything the car may make weird noises like it's squealing, sucking in air, that's normal, just rev it at 2kish revs and hold it there for sometime.
Also when you refit that big radiator hose, try to make the clamp sit in the same grooves it left imbedded in the rubber hose because there is slight chance it may have an air leak, also monitor the thermostat area for a few days, weeks and check if there is any leaks.