Ive recently replaced cows milk in my diet with soya milk and rice milk depending on what im eating or drinking (soya milk goes great in tea but goes manky in coffee). I have the missus to thank for that change, it turns out I really like the taste of soya milk though!
Replace soya milk with double cream, add 16 spoons of sugar to each mug and drink at least 3 litres, 12 mugs, every day.
If you dont like it sweet dont stir it
Really your body that is deciding what is the right weight for you, if you try to put on weight then it will just burn it off again unless you go to excessive lengths.
Example of a weight gainers diet
Breakfast 6 slices of toast with lots of butter and honey. Full English breakfast.
Lunch, fish & chips, burger and chips, etc. go large, no diet drinks.
Dinner, huge pile of buttered mashed potato with meat and veg. Sweet desert with double cream.
Add sugary snack bars, mars bars, full packs of 18/24 crisp packets etc. whenever you can stomach it.