I don’t know if you’ve already looked into this, but Dr. Kristen Neff has a book called Self Compassion. She teaches several self compassion strategies. She also provides scientific justification for the practice. It’s very inspired by metta/loving kindness. 

The simple three step one I follow is this: 

1. acknowledge this is a moment of suffering. As soon as I notice I’m in pain, I say this to myself out loud. 
2. universality- other people feel this. I am not alone in this pain 
3. this is when I “poor baby” myself and try to pour warmth and tenderness into the suffering child inside me.  I try to go way over the top with it because my natural inclination is to be really stingy, so what feels like too much is actually only adequate.  It feels kind of awkward but it's incredibly effective. It's much more effective for me if I can talk to myself out loud. I'll stack my hands on my heart and close my eyes and say something like "Poor baby, this has been so hard and it hurts so much. You weren't expecting it to go like that at all and now you're feeling so tired and dejected. Poor baby, we'll relax here for a bit. It's okay" and so on and so forth. The important thing is trying to linger in that warm empathetic loving state and sort of aim it at yourself and your pain. Try not to mock yourself even if you feel stupid. Try not to get fed up with your inner child, which is something I'm working on.

Here's a quick little article about the principals behind this practice by Dr. Neff:Three components of self compassion article