X1 Yoga 1st Gen - Compatible Digital Pens = fit in slot, charge

[bkl]

I have x1 yoga 1st gen and need to replace pen.

Want one that fits in slot, charges, and works well.

Is my only option to purchase OEM ThinkPad Pen Pro which came with device (and generic copycats from China) or are there newer, improved digital pens released after the laptop which are backward compatible, work better, fit in slot, charge properly?

Would digital pens included with x1 yoga 2nd gen, 3rd gen, 4th gen also work / fit / charge in the 1st gen? And are they superior to the pen issued with the 1st gen?

And would welcome recommendations on where to purchase a pen at a economical, reasonable price - used or new ok.

Thank you!!!!

Brian