The grey on the western wall looks dark and purplish on my monitor. It may come over as too imposing and monolithic on the southern face. If you're sticking with the grey palette then a warmer tone would suit the sandstone better. Does Dulux have a colour palette recommendation that includes your Berkshire White plus a grey? Check online or in store pamphlets. But, for such a big, expensive, and impactful paint job I would actually be tempted to get a colour consultant. You're not just repainting a loungeroom wall if it doesn't work!

Thank you Lesley...l always thought, Surfmist was more towrads white.looks like surfmist has some hint of grey..I might have to look for some other color which is more white than grey

Photos would help

Avoid paint as it wears. Stained or oiled timber would look great with a navy door.