Jonathan's companion, Lydia, would like to shed her armour when relaxing around the house at Breezehome in Whiterun. Jon has suggested getting down to her undies around the big fire in the middle of the living room, but she's not listening. I checked out everything in the store run by the two snotty sisters but there's nothing there that fits the bill, or her figure, for that matter. Any suggestions? (I've thought about sneak-killing a barmaid and taking her outfit but that seems extreme.)

Look for ancient nord armor, that is the armor that Aela the Huntress is wearing.

Classic answer - exotic and sixy? Forsworn "Armor".

Without a mod, followers default back to their stock armor when you they are not actively in your service. And, will only wear clothing/armor that is better than their defaults when they are in your service.