As a meditator myself I find that those who are interested in developing the skill of mindfulness within meditation as well as when outside of meditation is to be mindful in body mind and speech. As far as NoFap is concerned, during the reboot period to maintain mindfulness as well as not only avoid masturbation by the body but also avoid thinking about sex (mind) as well as not talk about sex (even talking about it in an educational manner). I find this will lead to a more successful reboot.
Can you share any tips for meditation and/or mindfulness? Especially the feeling in the body of letting go, tips on that and letting go of control, of the breath, thoughts, feelings and maybe tips on rest and sleep?
Given that you have exceeded 200 days I dont feel like I am in any position to give any advice to you. There are some good resources from meditation master Thich Nhat Hanh. Just type his name on Google and meditation and it will give you lots of resources on Mindfulness.