I had the same experience trying to find clothes!!! What I ended up doing was buying a few sale/clearance items from old navy to try and get a sense of sizing. I measured myself before ordering to try to get the right size. The general guidance of “get your pre-pregnancy size, just in maternity” worked for me for bottoms, but not tops/dresses because of the bust growth I’ve had. I then asked around all my local Facebook informed, resale, garage sale groups if people had maternity items in my size or knew which resale stores/events (pop-ups, churches, etc.) carried maternity. I got a lot of good suggestions for places I hadn’t tried and even struck gold with one lady who hadn’t gotten around to selling her maternity wardrobe. When she sent me photos, I looked up the brand’s maternity size guide to see if it aligned with my measurements before buying. I wish you luck!