Back when I constantly needed a pen I used to use a Parker espirit telescopic fountain pen, since it was the best small fountain pen that cost little enough that I wouldn’t mind loosing, but it was still small enough and good enough for my tastes. More recently since I stopped needing an actual pen with any sort of frequency it just kept getting dry and I just decided to stop carrying one.

This days the only thing that I physically write with any sort of frequency are ttrpg character sheets and for those I just need a good pencil, so I moved to the wsd magnetic 2.0 mm lead holder. I just love it both as a great mechanical pencil and a fidget toy

I use those and they have lasted me 5 years without issues, you just have to bend them to the side instead of out/in.

If you want anything more durable it would have to be nitinol for the superelasticity and memory effect, but as far as I know you would need to buy some thick nitinol wire and program the shape yourself, and that requires some specialised equipment

edit: spelling