Hello Carmen,
I'm still having treatment on my back, following a fall that I had many years ago, so I know something of what you must be going through. I'm now on first name terms with the staff at my local hospital though, so I might even get a Christmas card from them this year!
On a more serious note, whatever lathe you get will probably be made of cast iron, and so like me, weight becomes an issue, unless you can leave it in one place permanently. Further, why limit yourself to just pens when there is a whole world of miniature turning to be explored ??? I recently bought a Proxxon lathe, a DB250 which like other Proxxon power tools is meant for miniature work, everything from dolls houses onwards. This is the lathe by the way -
PROXXON TOOLS: Lathes - which as you can see is very light due to an extruded aluminium bed. Following their instructions, mine is screwed down to a piece of MDF for stability, but it adds little to the weight. The one disadvantage with it for pen turning is that the tool rest is also small, and so you would have to turn each half separately. This is a YouTube review by someone else who wants to turn pens on it though -
https://www.youtube.com/watch?v=aBtefIz7j7c
As I said earlier, please look into miniature turning, everything from Christmas tree ornaments to ornamental 'sculpture' work for want of a better name. This chap has a very small workshop, in what looks like a boiler cupboard. Forget the drill press and such like as he uses them for other projects, but he does all of his turning work on a DB250, even to making his own tools. (I cheated and bought a complete kit from Proxxon which came with chisels, chucks etc. as it was cheaper to do so from Germany than to buy just the lathe here in the UK, for some unknown reason!) He also made this though, for which he won second prize in an international turning competition organised over the internet -
https://www.youtube.com/watch?v=udCEeOfs7i8 It does show what such a small, light machine can do!
If you do a search on YouTube there are many more videos of miniature turning. I have just looked at my little library and found the following book titles though :-
"Small Woodturning Projects" by Bonnie Klein, which is exactly the same book as her "Classic Woodturning Projects", but one is published in the US and the other in the UK, with different covers as I found to my cost!
"Woodturning in Miniature" by Ian and Nina Wilkie. This has a very good introduction to miniature turning, but several of the projects are for dolls houses and such like.
"Small and Miniature Turning, a complete guide" by Ron Hampton, with a wide range of projects.
And finally "The Fine Art of Small-Scale woodturning" by William R Duce, which has many examples of exquisite decorative 'ornament' turnings and is probably the best book as you are an experienced turner.
Hopefully this will be of some benefit, but please let us all know what you decide please.
Tony.