Packmates.org is ok with NSFW stuff and it is run by our own Lemmy admin @Wander.
Number one rule with NSFW art on Mastodon in general? USE CONTENT WARNINGS! I cannot express this enough. Content Warnings let people know what the post contains and will keep it blurred till they have made an informed decision to click it to see the content that was blurred.
Also be sure to add alternate text that describes what is going on in the image itself. This is not so much for you as it is accessibilities for those with disabilities.