Middle Blonde to Light Blonde

Hey!

My natural hair color is a medium to dark blonde that's fairly neutral in daylight but can have quite a golden/brassy/gingery sheen in other lighting ???. I was told it's a 7 in depth. I want to go lighter, up to a 9.

A few years ago I've used box dyes that often turned out to be quite golden, sometimes ginger. I do not want to do the same mistake so I want to use 'the proper stuff'.  😉

I'd really like to use the Koleston 9.96 (pearly light ash blonde). I was told I would not need to bleach beforehand as it lightens up to 2 shades (7->9) but I should mix in some 9.16 (ash blonde) to counter all my golden tones that really come out when I lightend my hair. The desired hair color is a more purple/violet cool blonde which would suit my pale NC15 skin quite well. *whistle*

My hair is not completely virgin right now. 10 weeks ago, I got some highlights in the front, my hairdresser used bleach with pigment already included, so I guess she used a high lift color. The rest was 'glossed' with a cool tone and the ends got some mauve color/dye (I really do not know). She said the 'glossing' and colored ends would last up to 4 weeks, and eventhough I used some Instamatic Mauve 8 weeks ago, nothing is left (at least I cannot see anything but my natural hair color).

What do you think? Is this a sensible idea? Should I bleach beforehand? Should I do something else entirely? Does anyone have some experience with Koleston?

Thank you! *thx*