Mermaids

Mermaids is a UK-based charity. They seem to be very knowledgeable and sincere in desiring to help.

Why is it named Mermaids? Well, this is important symbology for many people in the trans community. Mermaids have a human upper half and a non-gendered fishtail lower half.

You can read a bit about that angle in this article:

Beauty Beyond Binaries: The Mermaid Trend Has an Extra-Special Meaning for Many Trans Women