L’Oréal Dia colour fading red

My hair has faded out very warm after 2 months of not colouring. I usually get dia colour in a 6

As I am breastfeeding and had a baby recently I struggling to find time to go to the salon.

I would love my hair to be a cooler shade, so looked into colouring with a 6.1 at home-

Will this fade to red again?

Should I switch to another brand with alkaline composition?

Recommendations on developer?