OP I think if you really want to focus on curbing your reliance on convenience / junk food you'll need to step up with the homecooking.
And to do that you'll need to break it down into manageable steps and to realise that if you live alone, you need to ensure that you're looking after yourself properly so you stay well & healthy.
I think your first step is to think about the sort of food you would like to be eating on a daily / weekly basis. What sort of things do you think you could manage ti cook easily? Start simple & work your way up to more ambitious dishes.
Do you have a cooker? An oven? A microwave? Cooking utensils? You'll struggle without these.
Start with only concentrating on one week at a time. Plan out what meals you would like to eat..3 x meals a day + snack.
For instance:
Breakfast: weetabix with milk + banana & tea or coffee x 7 mornings
Lunch: cheese sandwich x 2 days, soup & brown bread x 2 days, scrambled eggs on toast x 2 days, Gregg's pizza slice x 1 day
Dinners: buy a pack of mince & make bolognaise x 2 dinners with pasta & sprinkle of cheese. Freeze the rest for another week. Buy some chicken thighs & jar of curry sauce & pack of rice - chicken curry x 2 dinners & freeze the remainder. Baked potatoes x 2 nights with cheese & beans. Supermarket pizza on 7th night.
This way you end the week having eaten proper food & starting the next week with some meals already in the freezer ready to go. You keep rotating these each week.
But if all you have in stock is tea & coffee you'll have to build up a basic store cupboard. This will make making & planning meals far easier.
You'll need stuff like
Oil
Butter
Seasoning - salt & pepper
Herbs - mixed Italian is a very versatile one
Spices - you can build these week by week
Soy sauce
Honey
Jam
Rice
Pasta
Stock cubes
Tinned tomatoes
Tins of beans
Tins of fruit
Frozen peas
Frozen veg (if you've space you can get peppers, onions, broccoli etc which totally prevents waste as you only use what you need)
I think what you're looking to do is overhaul both your spending & eating habits & you can 100% do this.
I recommend looking at Jamie Olivers book online on how to cook as it gives a basic recipe for lots of favourite dishes + ways to tweak them to use up leftovers. I think it's an excellent resource
Good luck op!