I saw a question on reddit a while back. For reasons, they were looking for spinning wheel options that use only the upper body. I love a challenge!
I'm never going to learn that reddit is the place for one-sentence answers. But I also know that whatever is written there quickly fades away. So, with that in mind, the following was my (rather long-winded) reply. (spelling mistakes and all)
Exciting! I love this part of the process... getting ready for the next step and finding the wheel to best fit your needs.
Before we go too much further, I do want to mention that per minute spent a wheel is more efficient (and a spindle wheel like a charkha even more so), but like two pointy sticks vs the knitting machine, per day spinning, a spindle can easily out do a wheel. The portability and freedom to use every spare moment... but you're ready for a wheel, so let's get to that.
Using only upper body. I'm imagining a long draw (like a spindle wheel), using a distaff, or an e-spinner.
Charkha - especially the book (folding up version) is very good at cotton and other downy fibres with a staple length of under 2 inches and for spinning fine thread. I wouldn't say it is ONLY for cotton (saying that a wheel is ONLY for ONE SPECIFIC kind of fibre is my biggest bugbear! That and the modern trend of calling wheels "wool wheels" or "flax wheels"... It's simply not true!) is a mistake someone who didn't know spinning made a few decades ago and it's been parroted as truth ever since. (I'll cut the rant short there).
Spindle Wheels (a charkha is just one kind) traditionally (but not always) have a drivewheel that is hand-powered, and a spindle that we spin the yarn off the tip in a long (one-handed) draw. This is one of the oldest styles of spinning wheels and is extremely efficient! Miles per hour, I can spin more on this kind of wheel than any other.
A great wheel or Walking Wheel would be the European/North American equivalent. We also had table top versions but they were less popular. In much of the world, they have smaller table top spindle wheels (in India it's called a charkha, other places have different names).
These are great for fibres under 4" and were often used for wool and cotton in North America. Most of them have a stronger spindle and motherofall than a book charkha, so they can handle coarser fibres.
In Europe, when these first arrived, there was a strong rebellion against them because the yarn wasn't as consistent as people would like (learning curve took a while to get the quality up) so they quickly got the reputation that 'wheel spun yarn isn't strong enough for warp in weaving' which was parroted along the centuries to peak in the 1970s as "all handspun yarn is impossible to use in weaving"... sigh. (another long rant later... where was I?)
I know quite a few people who spin linen/flax on a spindle wheel as this technology is infinitely adjustable for the spinner's needs.
You can also adjust your method so that you can spin worsted-style using a distaff and different drafting techniques on a spindle wheel.
Spindle wheels are far more versatile than many people realize. I know quite a few novelty yarn spinners who have converted their flyer wheel to spindle because they can get the results they want.
A GOOD e-spinner will give you the largest variety of yarn possibilities. It lets you use both hands to spin the yarn. Good not only means well made (I'm partial to the Ashford ones, but there are many well-made ones out there) but a good fit for the spinner. If possible (and this goes for any spinning wheel) see if you can try one before you buy. Some yarn shops have them that you can use.
Adapting a treadle machine to hand powered: I haven't... but it sounds awesome. I would go with a Saxony style (big wheel to one side of the flyer). Cut the legs to make it tabletop compatible... or adjust them somehow for the right height for your body. Take the treadle and footman off as well. You could turn the spokes with your hand like a great wheel, but I almost feel I would reverse the wheel somehow so that the axel is facing towards me and I could put a handle on it.
Drafting one-handed isn't awesome on a flyer wheel. Simple to convert it to a spindle wheel... but there are ways to spin without doing that. Distaff mentioned earlier will probably be the best method. Long draw for woolen style yarn also works.
And I've written a huge essay. Sorry.
Let me know if you have any specific questions. I'm excited about your adventure and would love to learn what path you choose.