I have an idea for you Bee, that may help. Use Choice Architecture. I have been meaning to do a post on this - will get to it sometime. Place your gym kit already laid out before you go to work. Then, when you get back from work, just say to yourself...
1. All I need to do is put the gym kit on. Don't think anymore. (choice architecture - engineer the environment to make the desired behaviour easier).
2. Once you have changed, get your keys, go to the car, turn the engine on. That is all you need to do.
#2 is from a mini-habits course I went through. The idea is you don't actually commit to doing anything. Just doing those behaviours. If you don't want to then go to the gym, you are perfectly fine coming back inside. But in most cases, this is enough to just get the ball rolling.