Whew! The mitten fits, with only a little space at the top of it. I am more than satisfied. If, after wearing in proper mitten weather, I decide that it just isn't as warm as I want it to be, I'll knit a cashmere lining for it. That should do the trick! In fact, I might just do that anyway..... for grins and giggles.
The thumb was an interesting knit. Very fiddly, but fun. Picking up the stitches for it took some concentration; thanks to the hints/how-to's from the "I Make Mittens" group on Ravelry, I was able to suss out the whys and wherefores of knitting a thumb. Ravelry is the best. I was unable to follow the whole pattern ( I have stubby thumbs), or it would have been too long, but I think I did a fine job altering it to fit.
I still do have the task of weaving in the ends before it's completely 100% done, but that won't take long.