Help me fix my cooling system

For ages my car has had a problem where it takes ages to heat up, then will cool down again if I get on the freeway or whatever. The needle never stays in the middle where it should, it is always wandering around on the cold side of the temp dial. Car never gets too hot. This is because the thermostat is stuck open right?

What should I replace along with the thermostat?

It seems like it's best to do the thermostat, thermostat housing, crackpipe and whatever else all in one go. Like it's not worth doing one, best to do them all at once. Oh yeah and the crackpipe/oilcooler hoses. It never ends...

The Thermostat
The Thermostat Housing and connector, the pipeclamps & o rings.
Flush the system (new g12)
Check all your hoses (look for pink stuff around joins), change/tighten any pipeclamps, particulalry around the oil cooler

Thats it.... if its taking ages to heat up its usually the thermostat stuck open opened. You can also check and see if your temp gauge is working correctly...

Yeah sweet that is pretty much everything I thought of too.

I just wonder whether it is worth buying a new silicone hose set to go on at the same time, because apparently the oil cooler hoses suck to replace so it would be nice to get them done too, as well as replace any hoses that are just old and worn out.

Why not if you have the cash and time to do it... but remember you'll need to change o rings and those silly VW clips too...if your doing a flush you may as well... might be worth having a tube of gasket glue as well (just in case).

By o-rings I'm assuming you mean the ones on the crack pipe and what not? And the VW clips you speak of are the stupid oem hoseclamps?

What do you suggest I use gasket glue for? The block end of the crackpipe? Or the hoses themselves?

Yes, the ones in the pipe, and on any hose/flange connections you disconnect to drain/flush (even the temp senders etc)
Yes, those stupid OEM hoseclamps and the peg looking lock clamps.
Gasket glue is just a back up, if you stuff it up and/or forget a o-ring etc, you can gasket glue and limp it to get parts etc, although there are some people who do it anyway as some of the OEM flanges don't always come perfectly made or with good gaskets.
I've slightly spilt the end of one of my pipes into water pump getting it back on and gasket glue helped as a temp solution till i could get a new pipe.