Girl-mode shopping means shopping for outfits, not items. It took me a really long time to come to understand this (and I've mostly discarded it since transitioning my wardrobe) but it's important. Women's clothes are arranged and conceived in sets/themes/outfits, not by type of item.
This makes the initial shopping trip easier, though (actually this was the approach I took while I was transitioning my wardrobe - it works for guys' clothes too, it's just not as necessary). You go to the store - thrift store, department store, whatever you prefer - and you find one item that you really like. Or just pull something out of your closet if you have a few things you love, and wear it out shopping. Then you imagine yourself in the situation where you'd like to wear this item of clothing you've chosen, and you think of the most important pieces you need to wear with it. Assume it's a shirt, for instance - you need a bra, panties, and pants or a skirt just to be basically decent and presentable. So you find those. Spend some time, pick out the best things you can. Then think about the accessories - you need shoes, maybe a belt, hosiery, jewelry. Then imagine that you want to wear it in winter. You'll need a coat, gloves, maybe a hat. It seems like a lot of types of stuff, but you only need one thing of each type. When you're done, you have a complete outfit.
Some of the stuff you've bought can probably be mix-and-matched with other stuff you already own. You probably only need one or two coats for each level of formality you're concerned with, for instance. So the next time you go shopping you won't have to buy quite as many pieces. But it's important that each item you buy fits into a bigger picture somehow - you don't buy a coat because it's a coat, you buy it because you need a coat to wear with some specific set of clothes. If you buy a coat just because it's a coat and you like it, it likely won't really go with anything else, and you'll find yourself having to go out again and shop for an entire new outfit revolving around the coat. Which could result in something really nice. But it can get expensive.
Make a lot of shopping trips. Make them as small as you can. Never overwhelm yourself with new items that you didn't really try on together to see if they worked. If you just go out and buy a pile of stuff you think you need, you'll wind up with a closet full of clothes and nothing to wear.
(Pyjamas are the exception to this. They're worn by themselves, so you can just go buy pyjamas that you like and not worry about it. Underwear isn't an exception though - unless you wear something really unnoticeable like low-rise cotton G-strings, you'll need to select underwear that works under a particular pair of pants/skirt. And bras are even more important. If you don't plan to buy a new bra, then wear the bra that you want to wear with the shirt you intend to buy, even if you're not yet quite sure what that shirt is.)
