Don't replace an habit with another. Try to cut is all together because otherwise the habit is still there and you just change its characteristic and one day, the healthy habit will fail and you will be back to the unhealthy one. The same with there "healthy snack" to eat in front of tv because how long are you going to last with a celery stick or popcorn. One day, no doubt about that, it won't be a celery stick but a salty/sweet junk food because you will still be used to nibbling.
Decide that you will only eat ever at the dinning or kitchen table. Not in from of the Tv or while reading book/ internet. Eating is eating not munching without consciousness.
I am French, and we tend to only eat seated and never in the lounge or bedrooms (nor in the car, while walking, not on a bus,...) .
Treat as a noun has a very different meaning than the verb. You treat an illness, but your "treat" - the bad food that gives you pleasure is the opposite and is something deserved, I believe it only exist in the English language.
Go back to watching TV without putting something in your mouth. It will feel weird for a week, but if you manage to do it, you will be free for life.
Be conscious that you have been manipulated/educated into this behaviour. All the ads that shows happy people biting into a magnum/chocolate/whatever crap , condition you to associate two activities.
Also maybe stop buying what in France is considered children or party food. We don't eat crips on a daily or weekly basis. Chocolate bars are for kids not adults.
Every time someone mentions the French Paradox - we eat fat yet are slim - I want to point that it is not what happens at meals but in between or after that is the main difference. We don't snack. It is very frowned upon.
I know it is hard, because it is embedded since childhood. The snacking, the reward from food but this munching is only beneficial to the product manager who will reach his target bonus every time your hand picks a packet form the shelf. These foods, crisps and chocolate , are been designed in a lab to reach the perfect texture and taste that sends your brain banana. In nature, you don't have the combination of fat+sweet or fat+salt or fat+salt+sweet. Have you ever tried hot chips without salt. How many will you eat?
And the worst, is seeing all these mothers praising the melty puffs or veggies baby crips they give as great finger food to babies. How to hook a person to crap food for life .
Buy some nice new pillows, a rug, an ottoman to put your feet on, (maybe even a poster of the Tour Eiffel as a French reminder ) and make your living room a nice room you have no intention of soiling with crumbs or food stain or bad smell from greasy takeaways.
And before doing that, grab a plastic bag and empty your cupboards/drawers of all the cochonneries you have.