Sul sul! Here are some default replacement undies for your female sims! All are compatible with each other and you should be able to pick-and-choose for all of them. I didn't include saunatowel in these defaults because I honestly couldn't find anything I liked for it that would cover all the age categories and fit the themes. So I'm just putting it out there, if anyone knows how to convert clothing and wants to make their own default, the Sims 4 towels being converted would work wonderfully I think! Just an idea.

afbodylacylingerie replaced with @rascalcurious' 4t2 Conversion of joliebean's Guilty Pleasure Set, combined with iosiren's edited body mesh. Enabled for YF, untownified out of personal preference. Categorized as both "Underwear" and "Sleepwear". Barefoot sound. It requires The Sims 2: Kitchen & Bath Stuff in order to work.

efbodynaked replaced with @applewatersugar's 4t2 Conversion of Maxis' SP38 MeUndie. Enabled for YF & AF. Categorized as "Underwear" only. Includes the hidden "beige" swatch (unhidden + townified, it's the pizza swatch). Barefoot sound. Should be Base Game Compatible.

yfbodyunderwear & yfbodyunderwear_clone replaced with @platinumaspiration's 4t2 Conversion of Sentate's Chris Set (fullbody version). Enabled for YF/EF. Unhidden, townified, and categorized as "Underwear" only. Barefoot sounds. The clone outfit is the black swatch. Please be advised that this black swatch is the same texture as the one used in my female fried default, so it is only compatible with the clean / no dirt version of my fried default. It requires The Sims 2: University in order to work.

afbodyunderwear replaced with Goat's fullbody edit of SkittlesSims' 4t2 Conversion of Maxis' Base Game Scallop Bras & Panties. It uses iosiren's edited body mesh. Enabled for YF/EF. It includes the hidden "classicbeige" swatch which is unhidden & townified. Categorized as "Underwear" only with barefoot sounds. It should be Base Game Compatible.

tfbodyunderwear replaced with both @platinumaspiration's Sentate Chris Teen Conversion and Goat's SkittlesSims Maxis Scallop Bras/Panties. It uses the mesh from platinumaspiration for both underwear sets. It includes the hidden "purpledecal", which is unhidden and townified. Categorized as "Underwear" only, with barefoot sounds. It should be Base Game Compatible, but I'm not entirely sure for "purpledecal".