I don't know if this has been discovered yet so i'm sharing what i found...i did it with mjoll and haven't tested others yet but this is how:

First make sure your spouse is only equipped with their base equipment that you can't trade from them. Once your spouse sets up shop in your home ask what they have for sale and look in that list for their base armor/equipment (for mjoll it's banded iron armor) and buy that equipment from them...they should be naked now.

Now you can give them whatever clothes or armor you want them to wear and they should keep that on instead or stay in their undies if you prefer. Mjoll normally will only wear heavy armor but i have her in a dress, cooking home cooked meals...i've effectively tamed the lioness

I would recommend selling the base equipment to another vendor just to be sure it doesn't return

Nice, thanks! ....must try this on warrior hubby who insists on wearing unsixy armor to bed

Good find!

I believe you have to leave them one piece of equipment (for example, boots), otherwise the base armor respawns eventually.

Yeah, I've tried this before. It just re-spawns again.

I've taken Miuri's clothes a hundred times already. But every time I return home, she's re-spawned her crappy looking tunic dress again.

If I leave just her shoes, she'll just stay in her undies forever.

I've also given her Tavern Clothes but she never puts it on. Plus there are other clothes in her "store" inventory. She doesn't put any of that on either.

Kind of svcks. I can make my followers where whatever I want but not my wife?

hmm thats strange as i waited a week and went back and found her wearing the dress...i took all her armor but left the wedding ring on her, maybe that did it or maybe it was a good glitch for me?
I apologize if it doesnt work right but like i said i tried only with mjoll and it worked for me

You didn't take everything -- Mjoll also carries a random piece of jewelry.

I'll try this on Muiri, but as cobrasno1 said it respawns (what I've read also). The underwear thing might be OK, but I'd like to put Tavern Clothes or Vittoria Vicci's wedding dress on her. I've also read that if you marry Sylgja and have the top Pickpocket perk you can take all her clothes and she'll stay in her underwear. I just wish they'd wear stuff we give them or even rotate through several outfits in their inventory.

If youre on pc there is a nifty little NPC editor at the nexus. I've used it to redo my wife, housecarl and follower. It's very simple to use.

Yeah, I have no problem stealing anyone's clothes from them. I just can't get any of the non-followers to equip what I give them. They either stay in their undies (if I leave at least one of their original items equipped) or they re-spawn their original clothes.

Weird thing about Mjoll.......Her armor doesn't appear in her inventory when trying to pickpocket it. And I have all the perks. Everyone else (Lydia, Jordis, Iona, etc.) shows their armor in their inventory when pickpocketing but not her.

I checked Muiri's shop and her clothes weren't in her Inventory (she's, of course, not a follower) and my Pickpocket skill is at 76. If I level it to 100 to get the Perfect Touch perk I'll probably be like class-less level 70. Not sure I want to be quite that high, but what's 3 more levels at this point, right?

Granted they look cute in their underwear, but all-in-all I'd rather put them in nice clothes. I may have to compromise and settle for underwear and boots.

Equipitem works for me, unless the spouse is a follower + I use quickload while they're following me. It makes them revert. Not sure if it does while they're not following, going to test it out.

Yup, Muiri's been walking around my house in her underwear and boots for about a month now. But all my female housecarls are dressed in Tavern Clothes and gold diamond jewelry. They are always in their underwear when they are at home but as soon as I take them anywhere, they equip the Tavern Clothes and jewelry I gave them.

Mjoll seems to only want to wear either her armor or Daedric armor. I enchanted some Forsworn armor for her and she wont wear it. I wanted to see that body in Forsworn or Fur amour but she refuses to equip it.

NPCs can't utilize every Enchant that players can and people have said that when the NPCs 'decide' which armor is better than their current armor it's strictly based on the defensive rating - they don't consider Enchants. Can you improve the Forsworn higher than her rusted stuff?

I gave Mjoll a set of Thieves Guild armour (to match my own) using the console with "equip". She randomly wears it, but hey, at least she changes her clothes occasionally unlike most of the NPCs.

There are a couple mods that let you remove their default items (including the invisible hunting bow) and the items will stay gone. Definitely worth installing.

mjoll will only wear heavy armor unless you do this trick to remove her base armor...also the heavy armor has to be better then her banded iron armor or else she wont wear it. My mjoll rocks falmer armor nicely

But this should only be true if she still has her banded armor in her inventory right? If you take it away wouldn't she just equip the best thing she has available? All the other follower do this.

Lydia will equip anything as long as it's better than her default steel armor. But if you pickpocket her steel armor from her, she'll wear whatever she has in her inventory. Or whatever she has with the best defensive rating. In my case she only has Tavern Clothes in her inventory. So she wears that.

Why would Mjoll be any different? Weird.