Does Size Matter?

OK, I know this was discussed in here somewhere...but I can't find it
and now I'm a tad more than a bit confused.

I have worn a pair of 28.5 boots since forever. They fit just fine. So,
naturally, I've been looking for a pair of 28.5's.

Now, what I want to understand is this:
1 - Is the shell of a 28.5 the same as the shell of a 28.0 or is the
shell of a 28.5 the same as the shell of a 29.0?

2 - Depending on the above, which "boot" will have a thicker lining? If
the 28/28.5 is the same shell, then the 28.0 will have a thicker
lining, yes? If the 28.5/29 have teh same shell, then the 28.5 has the
thicker lining, yes?

The reason I'm asking is because I am finding better pricing in the
"whole sized" versions of the boot that I'm interested in, than I can
find in the "half size"...so, economically, I can save a ton of cash if
all I have to be concerned with is a good quality fit with a thicker or
thinner lining.