I spent many years trying to sound insulate band and recording rooms on the cheap. I’m not an engineer but from my experience you need mass to stop street noise, which has a lot of low frequency power. No amount of foam or fluffy fabric will make a noticeable difference. Save your money on the ‘soundproof’ fabrics, they’re no better than furniture pads, which can help a little but just aren’t dense enough to stop much bass. Best I’ve found for windows is particle board with chunks of tire rubber nailed on. But you probably don’t want to board up your windows so that’s probably not a good solution for you
I always wanted to find a heavy sheet of rubber to see if that worked but never found anything affordable I could repurpose. Also wonder if heavy muslin dipped in some kind of rubber material might do anything, but never tried that either. Maybe something like those flaps they use in commercial coolers, those are pretty dense, but a sheet. Sorry no specific recommendations for your case but keep a look out for any dense material you could fashion into a curtain or window cover.
But also just check around your windows if it they need any sealing. A tiny opening can transmit a lot more sound than you think.