Starting issue and thermostat

[Orbital]

Hi, I'm new to this group and I'd love some advice.
I have a citroen relay 2.2 hdi, it's about 7 years old and it's done about 90k miles.
The first problem is that it starts ok but is a bit lumpy/(misfiring maybe) for a few seconds until you give it a bit of a rev, I thought it could be glow plugs, the glow plug light comes on but only for a couple of seconds. Once it's running smoothly it's completely fine.
The other issue is that it doesn't generally sit at the optimum running temperature, unless it's being driven fairly hard. Most of the time the temp needle is sitting at the bottom. I assume that this is a thermostat issue.. Could anyone advise me about diagnosis and how easy is it to swap?
I'm not an amazing mechanic but I've done basic stuff for years, like changing head gaskets and brake calipers etc.
we don't have access to a ramp or any proper workshop tools.
Thanks loads for any advice.

[GiveMeABreak]

The glow plugs are really only used in very cold temperatures to aid starting - so this won't have anything to do with the vehicle once started.

Glow plugs can also be used by the engine ECU to assist with engine load to assist with getting the exhaust gas temperature up for assisted regeneration when necessary. Again, this won't be the issue as regeneration never starts when starting the car.

You likely have something else going on which may be a fuel quality / blockage or air issue.

Is it serviced annually? When was the last time the fuel filter was changed? If there's any hesitation or other issues, you really need to get it scanned, but yes, you certainly have an issue with the temperature gauge - so that needs diagnosing to confirm.