Tips/Tricks Online Shopping

Hey ladies. So I was wondering if anyone has any tips for finding items they are looking for online? For example, I'm looking for a 100% cotton turtleneck sweater, but a google search just brings up the same old brands like J.Crew, Everlane, etc. I know there are a ton of other amazing brands out there like Reiss, Vince, Ganni, Cos, etc. But they often don't come up in my searches. Is there some sort of aggregator that includes smaller labels? Also, I like to buy secondhand on Poshmark and other resell sites, but I find myself endlessly scrolling for hours and buying nothing. Again, I'm looking for mid to higher quality end brands for resale. I forget the name of these brands alot, and wish Poshmark would let me save a search with all these brands included and send me alerts when say a new sweater from Theory is listed. Do you guys have any tips and tricks for getting listing alerts, sale alerts, or aggregated searches for items? Please help!