Why are there not any eligible marriage candidates who wear Tavern Clothes???

Sorry, I guess Bethesda didn't want anyone marrying sixy women.

Seriously, I don't really know. There needed to be a few more marriageable options too, but unless you have a pc that's not happening. I assume you're an xbox or PS3 player.

I just wish that we could give them a gift like we do with the children. I would like my spouse to wear fine clothes around the house when they are not my follower.

^This for sure!

It can be done even on console with married followers . Give lydia clothes and take her armor. Not sure if it works with someone you marry but not follower

I don't have any perks in pickpocket and no skill, either, so I can't take her default armor. Thank you for the suggestion, though.

For a follower you don't need any pickpocketing. Start by giving her an armor that's better than her default, so she puts it on. Same with possible gauntlets and headpiece, but, and this is important, let her keep her boots.
Then you ask her what she has for sale. Her default equipment will have turned up in the shop. Buy them.
Then proceed by taking the armor you gave her away through the ordinary trade-things dialogue, and give her whatever you want her to wear.

Note that if you take ALL of her default gear, she will immediately revert back to default when you take the better armor away, that's why you leave the boots.

Also, note that she will unequip her given clothes if you dismiss her. You will likely come home and find her in her underwear (it was a bit disturbing when I had Brelyna streaking in front of the whole College. My first Breton however didn't mind coming home to find Vilkas cooking in just his loincloth ).

I will be thinking about Vilkas in a loin cloth for my second character Aussie, who after all this time is still not married. I would be worried about getting him killed though. Aussie was actually set on marrying Argis, but something seemed to have gone wrong with that plan, and I gave up on her ever getting married.

I wanted my first character Braggen to marry that sixy young thing wearing the tavern clothes over in Markarth, but despite hanging around for ages being hopeful, she would have nothing to do with him, I was disappointed

I used to worry about spouses getting killed as well, then a couple of things occurred to me:
1. Equipment. Vilkas wears heavy armor, for Pete's sake. Give him enchanted and upgraded ebony, dragonplate or daedric, and some fortify health jewelry, and he'll be virtually untouchable.
2. Potions. Always make sure there are healing potions in their inventory.
3. Save & reload. I reload if my character dies, why not when my follower/spouse dies?

The thing with Vilkas is that he will still do jobs for the Companions (with Ria) after marriage if you don't take him as your follower. I used to worry that he would get himself killed then, my Breton was more worried about the fact that he was roaming the wilderness alone with Ria, so I mostly had him with me and could keep an eye on him.