When looking into quality / quality of life items, personal preference becomes more important and way more options open up. I have a Parker Jotter, and I get the appeal but I have pretty big hands and it’s uncomfortable for using for more than signatures for me. I got into fountain pens last year and am falling down the rabbit hole, but they’re awesome. They’re often considered more friendly for people with some disabilities as they require much less pressure to write with, they’re designed to write under their own weight so you don’t have to press down to get ink on the page, which leads to less hand strain and cramping for longer writing like journaling. Neil Gaiman is noted for handwriting novels with fountain pens, even. There are all kinds of materials, pen body shapes and sizes, etc. so it is possible to get something that fits you just right. /r/fountainpens has lots of info/resources, but if you have any specific questions about beginner pens, general information, etc. feel free to shoot me a DM, I’d be happy to help!

This would be at least as comfortable as most fountain pens and as someone pointed out, it’s around $11, so it’s not an inexpensive pen, but it’s not an investment either.

Fountain pens write totally different. Honestly, the best advice is to just order a few different pens. Go on a stationary site, order a few different kinds of cheap pens, see what you like. Then buy a nice version of whatever style you liked most (gel/ink, rollerball, needle tip, fountain pen etc).

Fountain pens write totally differently though. You might have to relearn how to write. Honestly, I've no idea - a fountain pen might be easier or more difficult for you to write with regarding your disability. I'd check out some YouTube videos of people writing with them to get an idea of it first before buying one, they cost a lot more than normal pens.