Some things that might be useful or interesting

Cutting the Risk - Detailed discussion of safety considerations
The Hurt Yourself Less Workbook - A very non-judgemental tool for understanding and working with your self-injury. Some details about legal or psychiatric institutions may be out of date, but that's not at all the focus of the book.
The National Self-Harm Network - Involved in creating the two resources above, they also have a forum (if it's not be accepting new members it probably will be soon).
Newt's Safety and Care Guide - A general guide to the principles of safer cutting. Slightly reformatted from the original discord thread.
Self-Injury Support - Generally pretty cool people, they have a text, phone and email support services for women in particular. They won't just tell you to stop, even if it occasionally feels like that might be more because they know it won't work than because they don't think you should.