Why don't you just ignore the seats in B zone then, as that is the J cabin that 'disappears' when we have Mid J. Thats rows 11 to 14. That will allow for any config changes.

If your wife can manage the stairs, the UD is always J class, and so is C zone - that's rows 17 to 20. I would go for any of the aisle/window seats, so look at 17-20 AB or 17-20 JK. Row 20 is nice in that even the window seats do not have to step over a stool to get out.

I hope that helps and I haven't confused you!