I feel for you as l understand struggling with mental health issues and it makes quitting an addiction even harder but by no means impossible....lm living proof. I struggle with depression and before l quit l thought it would be impossible for me.....now l see l was building it up in my mind to an awful experience it didnt have to be and turns out it wasnt.
I think the suggestion of being active is a really important one. Maybe you can do exercises at home. A yoga dvd is a good idea and maybe some meditation to quiet the brain. Also l would start leaving the house by taking short walks and increase them. Maybe go to the shops for 5 minutes and increase on it when you feel comfortable.
About quitting.....it feels extremely overwhelming when you are battling mental health problems but it doesnt have to be. It becomes a mind over matter issue. If you look at it as youre just changing a habit and sit with the discomfort you can definitely do this.
I started by keeping a journal and reading a lot about quitting on the net, also reading many posts on this forum. Make lists......the reasons you want to quit, what you will gain from quitting, why you hate smoking etc and very importantly a list of coping strategies. Refer to these when youre having cravings . Journal how youre feeling or even better write it on here so you can get support.
Are you planning on using any nicotine replacement therapies? I use the nicotine spray and it has hleped me tremendously. I dont think l could have done it without it. Keep busy in the early days with things you enjoy. Cravings come and go. Honestly l didnt find the first couple of weeks as hard as l expected it would be. Arm yourself with mints or lollies....something to suck on when a craving hits .
If you really want this and you sound like you do, it is within reach. Good luck and keep us posted