I specced my car and had to wait a long time (4 months) as it was only just starting production. It did mean I got a very good deal.
Along the way, they changed the base spec and added heated seats. I too have back problems, and it is absolute bliss some mornings to be able to have that heat.
I also ended up with other extras that were bundled with ones I definitely wanted. I needed a rear camera because I have a neck problem and no left eye; it came with a front camera too, with lane departure warning and automatic speed limiting on recognising speed limit signs. I also requested some other 'extra' and ended up with the semi automatic 'self parking'.
And although I didn't specifically want them, they are good to have.