A ham sandwich and other processed meat definitely should be an occasional part of your diet, not every day. Aim for no more than once a week.
Pasta or cous cous salad, or slice of Spanish omelette or similar instead? I once made a massive one in an oven tray that was very easy and made 4 large portions.
Have sandwiches a couple of days a week but with egg, tuna or leftover roast chicken on wholegrain/seeded bread?
Instead of chicken kievs have marinated fresh chicken or chicken breast topped with tomato sauce and cheese? Of course, you could make your own chicken kievs, but that sounds fiddly and probably a step too far in the beginning.
If you buy yogurt, just get plain full fat Greek style and have with a drizzle of honey (or make your own fruit purees, they freeze well in ice cube trays) and/or dried fruit, nuts and seeds.
But it's hard if you're trying to feed a 'ham sandwiches and sausage and chips' person because that's very easy and that type of food is very palatable and probably addictive so they'll often just refuse to eat healthier food. How old is DS and how do you think he's going to take the move away from his beloved ham sandwiches?