Absolutely classic signs of a failing thermostat. What usually happens is that a rubber seal inside the thermostat perishes, allowing coolant to flow when it should be fully closed. The problem gradually gets more noticeable as more of the rubber seal disintegrates.
Replacing the thermostat will completely fix this and it's a straightforward job. Just remove the battery, unbolt the ecu, unclip the wiring, swing the wiring out of the way (no need to disconnect anything apart from the battery), remove the battery tray and you'll have all the access you need. Syphon out enough coolant to drop the level below the thermostat housing; if you are careful and work cleanly, you can pour it back in at the end of the job.
On models up to and including Euro4, less than £10 all in. Euro5 and later engines have a themostat with integrated temperature sensor (also known to fail when the plastic spigot disintegrates; more serious since you also lose the coolant) which costs about four times as much.
If I remember correctly, it was a little easier to remove the coils as well. M6 bolts with 10mm AF heads. Don't over tighten them.
Depends on the age of the car; they've moved around the engine over the years. If they're in the way, just unbolt them, leaving the leads attached.
The less you disturb, the less likelihood of something else being wrong after you've finished the job.
