We do not want to be forced to wear the dreadful pajamas in Skyhold!

Simple soltution in my opinion, put a wardrobe in your otherwise redundant quarters a new tab in the armour customisation "casual" buy the designs cheaply from the guy in Val Roueaux that sells the cosmetic upgrades & done, you can now completely choose what to wear casually through Skyhold, as

for the design themselves, just take the noble & commoner outfits that the NPC's wear, no major additional work needed.

Just my thoughts