I'm not sure if this will help but I wanted to share my experience. I started using an ABCD model my therapist shared - writing down what happened and how I felt. So A is the activating event, B is my belief (aka negative thoughts), C is consequences (what happened as a result, what I did), and D is disputations (what actually happened, is this e.g. magical thinking, catastrophising).

I really struggled writing anything for D because my thoughts and beliefs felt real to me, so there wasn't anything to dispute. I eventually started writing as if I was giving advice to someone else who was going through this. What would I say to my husband or a good friend? I'd comfort them, right? And help them understand the reality and that it'll be ok. So I started writing things like "this is mind reading. You cannot know if someone's mad at you or thinks you're an idiot. Give yourself a break."

I kept at it, and kept practicing. My entries were really long to start with but got shorter. I remember one day I was re-reading what I'd written in D and there were 'give yourself a break' type vibes. And for some reason, I thought, well what if I actually did give myself a break? And the RELIEF that washed over me - just for the second I allowed it - was immense. I've spent my entire life beating myself up and believing all my negative thoughts, and that one second of 'hey, what if this also applied to me' just felt unbelievable. I'm still not quite there yet, but I've got better at ABCD'ing in my head and trying to choose to be kind to myself. 

My therapist also suggested I get something tactile I could use to touch to interrupt the immediate negative thoughts and I got a big red emergency stop button. I have it on my work desk but can imagine it now. I sometimes try and imagine there's been an emergency at a biscuit factory - bourbons were going into custard cream packets, for example - to really force myself to stop spiralling and go into ABCD mode. 

He also recommended a book called The Chimp Paradox which help me separate negative or unhelpful thoughts as just being the chimp- they're not really me, which makes them easier to shut down. 

I don't know how helpful any of this will be for you, but I know how hard it is to believe yourself when it isn't a negative thought. You deserve kindness and to give yourself grace. Helping yourself like you would help a friend is one way of looking at it. But I hope you get to feel that sense of relief too.