I always use cheap, own brand white matt emulsion thinned 25-30%, apply 2-3 coats in quick succession; dry overnight & then apply your chosen finish. Nothing stopping you using your yellow top coat as long as it’s standard matt emulsion, non vinyl, non washable & doesn’t have a high acrylic content but the mist coat colour really won’t make an awful lot of difference to the top coat coverage. If its quality paint, you may need to thin more than 30% as it needs to be thin to soak into the microscopic pores of the plaster & provide a good key for the top coats, otherwise your paint will either eventually fall off or come off in sheets with any wallpaper subsequently stuck over it!
You must leave a skim a minimum 10 days, base coat + skim for 28 days to dry out.
I used to use the supermatt, but could not tell too much difference between that and a Macpherson paint, other than the price. However, when it comes to glossing, or finish coats, then I will switch back to Dulux.