Hi all - unsure what to do about hair dye! Any advice appreciated! :)

[stephy190]

My hair has never been dyed (used to dye it with box dye 10 years ago - but current hair I have is all natural)
My hair is very long (hip length) and has a few greys starting to appear through it - it's not a block of grey yet but some strands scattered throughout
I will want to start dying it soon if the greys start to become more noticeable, but I don't want damage or awkward demarcation lines and I want low maintenance.

Do you guys have any advice for me? My hair is a medium brown and I wouldn't mind going a bit darker. Advice I've had so far is to go and discuss with hairdressers but I know that could cause damage getting hair dye done at a salon. I used to use lush henna but they have apparently changed formula now and have bad reviews for them!

I have no clue what to do and I don't want to make a mistake as I have very healthy long hair - I know brown dye is less damaging than bleach but I don't want to risk a lot of damage but would just like some grey blending and a little tad bit darker without having to constantly maintain it! I guess I'm wondering would semi permanent be enough for my greys and would it be that damaging?