What would be the opposite of "sexy clothes", as in "clothes that hide sexual bits" ? Like for a woman, a top that would hide and make her breasts much less pronounced?

Thanks in advance.


OED

Modest

  1. (of a woman) dressing or behaving so as to avoid impropriety or indecency, especially to avoid attracting sexual attention.

    ‘the modest women wear long-sleeved dresses and all but cover their faces’

I think modest clothing conveys the meaning you're looking for.


Frumpy

Defined by Merriam-Webster as:

dowdy, drab

and perhaps more relevantly by the Urban Dictionary as:

A female with lack of concern for appearance. Often characterized by sweatpants, frizzy hair, gramma panties and a paisty complexion.


Demure defined by the OED as

(of a woman or her behaviour) reserved, modest, and shy.

(of clothing) lending a modest appearance.

is a suitable antonym for "sexy".

Interestingly, however, the Collins online dictionary includes the suggestion that demure clothing and actions can be adopted to increase attractiveness in this entry:

If you describe someone, usually a young woman, as demure, you mean they are quiet and rather shy, usually in a way that you like and find appealing,

She's very demure and sweet. The luscious Miss Wharton gave me a demure but knowing smile.


Wholesome 2. Conducive to or promoting social or moral well-being, especially in reflecting conventional moral values: wholesome entertainment; a politician with a wholesome public image.

and/or

Conservative
​ If you are conservative in your appearance, you usually do not like fashionable or modern clothes or hairstyles: He's a very conservative dresser - he always looks like he's wearing his father's clothes!