Is there a way to improve them so that lydia or someone else would wear them(xbox) without pickpocket or marrying them/sellibg default. Those methods turn into nightmares when they run around the house with not much.

Can i improve the armor so that they will choose it when given?

only to someone who wears light armor I'd think, lydia uses heavy

Smith the krosis out of them? I hear they'll wear anything with higher AR than their current armor

I always thought they would wear what you gave them providing it was better then their default armor. Like Farkas for example. He wears heavy armor but I know I've seen pics of him wearing forsworn. Even fur. But come to think of it the person showing those pics did say they were married...

Either way. As long as its better then their default they should wear it.

Just Smith it up to Legendary, and enchant it (optional) and they will wear it right away.

Simple.

'Tis a little cold in Skyrim to have her wearing that don't ya think?

I kid. Lydia's a Nord. She could run around in her undergarments and wouldn't be bothered by the chill. If a buch of Reachmen can handle it, you know she can.

She should put anything on if you smith it high enough. Try using a potion or some enchanted gear if your smithing skill isn't high enough to put it past her current set.

1. Find a follower that specializes in Light Armor* (ie. Frea, Jenassa, Serana, among others).
2. Improve it so that it has a superior AR than whatever it is they are already wearing.
3. Stare at your follower's mammaries, you pervert.

*Though it's possible that followers who do not specialize in LA will wear it anyway if the AR is higher than their default set. I cannot confirm this.

Aela wears heavy and I've gotten her in forsworn before.

She's skilled in light armor, not heavy. You have to look at their skills, not what they wear. There are several others who are mismatched as well:
Erik wears heavy armor (iron), but has high skill in light and none in heavy.
Farkas wears heavy armor but has low skill in it, IIRC (and none in light).
J'zargo wears robes but has heavy armor skill.
Among others.

The USKP fixes Aela so she has some skill in heavy armor too. And I think ESF Companions change her Ancient Nord Armor to a light version, but I'm not sure.

As for the smith-it-to-legendary, I'm not sure it works. At least followers used to look only at the base AR and not st the improvement. I think it's possible patch 1.9 fixed it, but I still have a feeling they only care about base AR in my game, so I'm not sure.

Aela specializes in Light Armor.

EDIT: ninja'd