Well, to meeeeeeeeee......lol....extensions seem an expensive way to go if you can actually grow your own hair?
The Henna effect washes out on a few weeks, so unless you just colored your hair, you should be just fine.
With your hair dark, you will have to bleach it white to dye it a pure purple, is that what you were thinking?
What about clip in extention-esque pieces of hair you can take in and out rather than actually getting anything sewed in?
Condition condition condition
and
35 is way young, have a blast with your hair!