Hi heavenly, what really occurs to me reading your description is that you've fallen out of love with food! Which is a shame. I think by slowly adding in lovely fresh ingredients you can turn that around.
And, just like many of us here, you have trouble giving time and energy to look after yourself. But you need to learn. You are important too!
Sleep (who has become something of an oracle on this thread :o) is spot on about eating three meals. I no longer generally eat straight away in the morning, but I've ditched my beloved cereal in favour of eggs. I usually have two boiled eggs with one slice of toasted really nice seeded wholemeal bread and proper butter (not spread). It amazed me how quickly I've grown to love it and I look forward to it every morning now! I vary it a little - your idea of mushrooms and tomatoes is great.
Here's a few changes you could make - just do maybe one or two a week and it'll be sustainable and not overwhelming (IME):
Drop one cup of coffee.
Breakfast as mentioned above (I eat mine between 9 and 10 as I'm ready by then)
Look for 'fake' foods in your kitchen and replace one when it runs out - eg spread for real butter, artificially sweetened yoghurt for whole Greek yoghurt, processed/low fat cheese for proper decent strong cheddar (probably more expensive but you won't need as much)
Get some whole unsalted nuts as a decent snack.
Put some avocado in your lunch or dinner (it's a superfood IMO :o)
Cut up some carrots/cucumber/pepper etc to have with your lunch.
Try one new recipe a week with lovely fresh whole ingredients (we can suggest stuff)
Make soup for lunch - if you have a big pot you can make enough for a few days.
Get some berries if you want to try fruit - I find a small amount very satisfying as they are strong in flavour and things like blueberries and raspberries aren't so sweet.
Ditch the lunchtime crisps or maybe just put a few on your plate and put a clip on the bag.