Hi Belly
1) You could use
to get as well. Both the full infinitive (to get) and the plain/bare infintive (get) are correct after
do in sentences like yours. There is an old song
All I Have To Do Is Dream. It could just as well be
All I Have To Do Is To Dream.
2)
Not [a single] one is idiomatic and grammatical.
Not any fitted is impossible because
fitted is the finite/main verb (past tense) and the collocation
not any/anything/anybody is never used as a grammatical subject.
Not + any/anything/anybody is possible when
any is
an object:
I didn't see any boys there.
I didn't see anything there.
I didn't see anybody there.
3)
Should is a defective/modal auxiliary and is therefore
always followed by a plain infinitive:
Should your information turn out to be true, ... However, the sentence is incomplete as there is no main clause.
CB