Brassy highlights help please

[JMApril]

Hi there, I have a base colour of 5 -6 which kicks out a lot of warmth - golden - when lightened. I have had an allover 7N tint for around 2 years now and then over the summer had fine highlights three times on the top layers at the front and sides - I think 6% 12N was used but not 100% sure of this. Now, my hair looks a little skunky(!) as the highlights have built up and have gone practically white at the ends but have an overall yellowish golden cast. What I would like is a more copper colour if possible but still fairly light - certainly no darker than a 7 and maybe even an 8 if possible. I've had a few colour consultations about it and have been told I would need to have more highlights to achieve the look I'm going for as tint can't lift tint. My problem is, the highlighted areas of hair are really damaged. If I look at the diameter of just a normal 7N tinted hair and then the diameter of a highlighted hair, the highlighted hair is probably half the diameter. So I'm really not keen on any more highlights particurlarly as I'm due to give birth next month and am terrifed of the potential hair loss that goes with that being exacerbated by highlights.
So, I was wondering if anyone can suggest anything a little gentler. The overall look I'm going for is probably Sarah Jessica Parker's current hair colour - front cover of SHE magazine at the moment. It's probably an overall 7/8 with warmth but still a few highlighted areas peaking through. Would it be possible to achieve this by putting an 8N tint on my roots and then working through some kind of copper toner or semi as lowlights and then leaving some of the highlighted areas alone? Then on the highlighted areas that have been left, could a toner be applied to them to take them from golden to copper but still have the same lightness? Sorry, loads of questions! If anyone could help me out, I would really appreciate it.

thanks

Jacqueline