I didn't have any luck blending my natural hair with a synthetic hair topper, but have seen really good ones on other people! The texture was just too different from my bio hair. I found a seller on etsy that does curly human hair toppers and then added some extra hair for more volume. My hair is thin enough that it can really only operate as the thing that blends my hairline and nape. To ease into things, I stayed as close to my natural hair color and texture as possible.
Here's what I bought: Topper: https://www.etsy.com/listing/1116651254/biscuits-13x13cm-base-human-hair-topper?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=human+hair+topper+biscuit&ref=sr_gallery-1-11&frs=1&organic_sear...
Additional hair: https://www.amazon.com/gp/product/B089RW8JD5/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1