I suggest you keep looking at the shelters - something you like *will*
come along.  Part-bred cats are often from kitten mills and I'm sure you
don't want to encourage that kind of breeding.

I have never heard of 'Manx Syndrome' - maybe you could post the URL
where you found the reference?  What I *do* know is that the short tail
in Manx cats is caused by a single gene which is dominant e.g. the cat
only has to have one copy of it to have the short tail, and if two cats
with the gene mate it is fatal to any kittens that inherit two copies of
the gene.  However this is fatal before birth, not later on.

BTW if you are paying for the kitten and all it's care how come what
your mother likes in terms of colour has anything to do with it, unless
you are dependant on her?

Also, if your mother insists on declawing (I suspect you still live at
home) please, please wait until you are living independently and it's
your call.

The final thing to remember is that losing a cat hurts however old it
is.  If it's a good old age that's a comfort but it doesn't take the
pain away.  Those of us that continue to keep cats after having lost
them take the view that the pleasure they give during their lives
(however long or short) outweighs the pain of their lose.  Put another
way, nothing venture nothing gain.  I lost two cats at 6 1/2 and 7 to
cancer, but knew that although I couldn't replace those individual cats
I *had* to replace the general cat-shaped part of the hole they left in
my life.  The bits which were particular to them are what was special
and irreplaceable about them.  I still feel weepy looking at many black
cats (Sooty was pure black) but there is no way I could contemplate a
life *without* cats.