I think that any positive thing that allows you to express your feelings is a good alternative to self-harm.
When I would self harm it was because I felt really shitty about myself, so I began to use different methods of self-care to replace those old behavior habits. I would take a walk, take a hot bath, visit a friend, draw, paint, take a nap, etc, etc. Anything that helped me to care for myself or that took me "out" of myself for awhile was helpful.
Also Identifying those thoughts that led to my crappy feelings helped too. I eventually discovered that it was due to negative core beliefs such as, "I am bad," "I deserve to be hurt," "I am not as good as others," "I am unlovable, unworthy" etc., etc. Stopping those negative thoughts and replacing them with positive thinking is very underrated when it comes to PTSD methinks..
Now I never get the urge to self-harm anymore. Now when I feel bad, I think "I am a good man," "this bad feeling is temporary," "I will feel better soon," etc. It may seem like a small thing but it really worked for me and I hope that in the same way it will help you too!!!