[Rob]

I'm very much in the development phase and ultimately looking to use an Ardunio Mega 2560 Pro as the heart of my system which necessitates some delicate soldering. I currently have a 50 year old real of solder of unknown spec and the cheapest variable temperature soldering iron on the market, so good that the manufacture haven't even put their name on it. I have rapidly learnt that these do not give me the precision and control that I need. Can anyone recommend me a suitable soldering iron and solder, whilst I appreciate that I need something better than Amazon basics I don't want to invest thousands in the top of the line Weller, I've a feeling that for what I want there's a sweet spot between the two but I don't know enough to know what that is.

[DStage]

Hi. I'm probably too used to old methods or too lazy to look for newer alternatives so might not give you the best advice
My proposal would be any reasonable clone (meaning actual clone of the electronics) of the good old "936". Just type something like "936 soldering station" and you'll get many brands making same thing for decades now. It's cheap and gets the job done mostly.
Of course these days there are plenty of not bad clones of other systems too, bit more expensive than 936 but still very afordable and arguably better. But I won't give you anything specific here.

As for the solder, it easier to use a leaded one so anything for electronics between let's say 0,5-1mm with flux cores. Going below 0,5mm in my opinion is almost never useful. And 1mm may be on a thick side for smaller elements (not because of the size but rather the low amount of solder they need).