about the necklace idea.... it's a great one. And don't just think necklaces, expand to cool, funky accessories of all types that are really *you.* With fluctuating mama-bods, you gotta think outside of clothing items that depend on your waistline to fit right. My favorite one is scarves. A fabulous scarf can be the one statement piece in your whole outfit that really makes you feel put together and stylish. The outfit itself can be solid colored basics that are as flattering to your shape-of-the-month as possible, but the cool scarf really stands out against it and draws the attention (perhaps away from whatever it is about your bod that you're not thrilled with just yet) and can also be used as a nursing aid, to drape across the chest above the breast and shoulder, for example, if your clothes don't keep that part covered when you are breastfeeding.
Second favorite accessory, for me, is shoes/bags. Cool boots or platform strappy sandals that really speak to you don't care if you gained weight with pregnancy and can add so much pizzaaz to what you are wearing, especially if it's just a pair of leggings/capri leggings and a tunic. The bag/diaper bag can be bright and nifty, blingy or whatever, and if your outfit is simple and solid colored, the bag/diaper bag can be the part that makes you not feel frumpy when you step outside your home.
Jewelry is also excellent, dangly earrings or cool necklaces (or bracelets, although these annoy me) of all types, even durable ones that can handle kiddos grabbin' on them (for the most part). There are infinite options, so you can find ones that look great on you and fit the style you truly want to exude.
Of course you still need to choose a hairstyle that you think will work great, but the wig idea was a great one, so you can test out a look on your face shape and skin tone. a drastic cut takes a lot of time to grow out and a major dye job can wreck the quality of your hair especially if you have to re-dye it if it doesn't work for you. A really good stylist can recommend what would look good for your face shape and skin tone, or just browse the internet and try to find photos of women who have the same face shape and skin tone and a hairstyle that you're considering and see how they look. There are websites that walk you through these decisions and recommend certain cuts and colors for your type.
You still gotta wear tops and bottoms (or dresses), and I know it's hard to buy for a changing body type. But there is a wonderful solution---wrap tops and wrap skirts/dresses! I love that they can be customized to perfectly fit the body you have today, and OH SO FLATTERING. The wrap/tie bit is usually at the empire waistline, absolutely the most flattering spot to cinch an outfit when you aren't sporting your trimmest waistline at the moment. Get a few basics in dark colors like plum, navy, hunter green, and of course black (these are the easiest colors to wash out messes that little ones cause on your lap as well as the most slimming) that are quality and fit wonderfully, in washable fabrics. I prefer 98% cotton/2% spandex.
Budget issues........eBay! I second the eBay notion! I buy second hand clothes listed on consignment from a few trusted ebay sellers that I use over and over again the past decade. Or just from whomever has a lot of positive feedback. There, I can find items for 95% off retail and the selection is UNBEATABLE. Whether it's a scarlet red stretch cotton wrap blouse or a stretch denim wrap dress or a silk scarf in a print that excites me, or jewelry/bags/shoes of any type, I can always find amazing bargains. Almost my entire closet is bought from eBay and I laugh at clothes store prices when i am in one, and imagine how many items I could have from eBay, for the price of one item in a brand name clothes store.
etsy is amazing but only for pricey splurges.
Good luck finding a style that makes you feel amazing when you look into the mirror before walking out the door!