I second that. I got mine on amazon before I got my phone and it's exactly what I was looking for. It was around $15, thin, decent looking...
Edit: https://www.amazon.com/gp/product/B0789S2LZH/ref=oh_aui_detailpage_o02_s01?ie=UTF8&psc=1
It still shows up in the Play Store for me, under My Apps, probably because I purchased it ages ago:
https://play.google.com/store/apps/details?id=com.nuance.swype.dtc
Last updated Jan 2018. Fine on the S9+ Oreo and Pie.
And no, Swiftkey doesn't come close.