At the moment i'm using a
Pilot Hi-Tecpoint V5 refillable (
https://www.pilotpen.eu/en/collectio...-fine-tip.html). It's a roller-ball pen, with a needle tip with a bib 0.5mm. At the beginning it writes as small as 0.3mm, but once the tip is worn-out it starts to increase to 0.5mm and over. Pressing very hard will wear the tip faster and also bend it, and once these are true, the pen will no longer write continuously. That's the queue to replace it.
Refilling these is straightforward: they use a 1ml cartridge which can be bought, but is much cheaper to be refilled. To do this, just use a syringe and refill the cartridge again.
So as long as you do not drop it (the tip will bend), or press hard, it will last you for years.