Vanity sizing is actually incredibly degrading.
My feet have always been all kinds of messed up. 80% of the time, I'm a toe-walker, which has made wearing flat shoes painful (Sorry, beautiful Rachel Comey creepers I wear about once a month because they give me charley horses in my arches). The other 20% of the time, I'm heel-striking so aggressively that I have had to resole and reheel shoes THREE TIMES over the course of one winter (Sorry, beautiful Acne boots). Oh, and I've also had hammer toes pretty much since birth, because I am a beautiful and dignified creature.
That was all well and good, and I was coping, until it seemed like one foot grew 3/4 a size overnight a few years ago. I was running to an event at Lincoln Center and realized I was not dressed quite formally enough, so I stopped into an H&M, grabbed a cheap pair of heels, stuffed my feet in them, and then mentally berated myself for grabbing two different sized shoes off the rack in my rush as my right toes begged for freedom.
Except they were exactly the same size. Eight. Yup. I returned them anyways, thinking they were mislabelled or badly made, only to have the same thing happen with every pair of heels I tried on in the store. An eight and a half was just a little snug on my right foot, but the eight fit fine on my left.
I immediately thought I was pregnant. Okay, calm down, I know. That seems like a bit of a reach, but I remembered reading that women's feet would grow during pregnancy and maybe that was lopsidedly happening to me? I used my store credit on a sweater, then bought a pregnancy test on the way home. It was negative, obviously. I don't know what or how it happened, but now my shoe size is eight on the left and eight and a half to nine on the right. Shopping for shoes can be a bit of a problem, but here's how I handle it.
1. Deal with it
The size discrepancy with my feet isn't super huge, so a lot of times I can just deal with it, especially with boots or sandals. I'll buy an eight and a half and stretch out the right shoe a bit by putting on some thick socks, then the shoe, then blasting it with a hairdryer. You can also soften up new sneakers to give them some flex by throwing them in a dryer on low with some tennis balls. That lace-up sandal trend that was really big over the summer (like these) was a godsend, since I could just loosen up the straps. I'll also mismatch my socks so that I can bulk up the left foot in a shoe that's about half a size too large for it with thicker hiking socks, like these.
So this has lead me to tentatively ask my roommates "Does... anyone need... a single right insole?" multiple times. The answer is always no. Someday I will find a man who has been trying to offload single left insoles his entire life and we'll basically have to get married. Hopefully our kids will have symmetrical feet.
The important thing to remember is that you want stiffer sport insoles rather than the squishy gel ones, since the aim is to basically give you an extra few centimeters of material that's similar to the sole of the shoe for your smaller foot. Plus, nothing makes you feel more unbalanced and vaguely squicked out than having one single squishy shoe that is also too big.
Make sure to take stock of where in the shoe it's too big. It might be just in the toebox, or the heel, or both. You can find specific insoles that are extra-cushioned in those areas by grabbing ones that are targeted to pain in that area. Sometimes I just stick a few of these ball of foot cushions in the toebox to bulk things up. Don't be afraid to stick them around the top of the inside of the shoe, too! A podiatrist can also make a custom orthotic for you with a toe filler, but if I do that, I have less money for Acne boots, soooo.
3. Make capitalism work for you (kinda)
Please do not be the person who checks out with an 8 and a 9 in a size 8 box, hoping the sales person doesn't notice. Retail workers get in trouble for that shit, and there are other ways to do it.
I don't find that I can jigger high heels to fit correctly on my own, though god knows I've tried. Having them even slightly too big means I get tons of heel slippage, and I'm never able to hide the insoles I'm using.
Luckily, Nordstrom does split sizing. If you're in-store, you can just ask a sales associate, and they'll help you. If you buy online, you buy two sets of shoes, then return the ones you don't need. It's a little bit of a hassle, but shipping is covered, and it's significantly less of a hassle than spending your sister's wedding without bloodflow to your right foot.
When I'm not looking to spend a ton on shoes, I'll generally buy two sets at Forever 21 or another cheap store (I know, fast fashion is terrible BUT), and then donate the mismatched pairs to the National Odd Shoe Exchange, which helps amputees with footwear.
Anyone else out there have different-sized feet?