Why are Costa or Starbucks lattes so good? I’m a coffee addict and I have been always having Starbucks as well Costa. I just love their lattes , but it become too expensive over time, so I am on a road to discover how to make coffee like them.
What I have tried so far:

I have tried Nespresso machine (problem is the pods are stored for ages which make coffee loose its flavour),
French press (feel too watery) and
Milk instant coffee (where it is full cup of milk with one spoon of instant coffee)(which feels too heavy) or
instant coffee (which feels fake like boiled water).

I am tired of all so these failed attempts, so I go to Costa everyday and I always have a latte. There’s something about them that make coffee so good and alive.
How can I get that without being too expensive? But without compromising on taste? In short, why do those coffee shops have such amazing coffee?
I'm not familiar with Costa, but I am with Starbucks. Let me offer my ideas in what's different.
Starbucks stores use fully automatic espresso machines with semi automatic frothing wands. The espresso machines make true espresso, unlike all of the brewing options you mentioned. This is the main reason the coffee is better.
The frothing wand also uses steam to froth the milk which creates a wonderfully creamy texture in the milk. Stick and pitcher frothers can't make the performance.
There's also grind. Starbucks stores use high quality coffee grinders that grind the coffee quite consistently. Coffee used for espresso is ground on demand for each shot. Your coffee at home might suffer if you're not grinding right before your brew or if you're grinding with a lower quality grinder.
Lastly, drink recipes. Starbucks cups are printed with volume markers to help baristas match recipes exactly. When you buy a latte at Starbucks, the ratio of espresso to milk is ideal and is the same every time. Unless you're measuring at home and know what that ideal ratio is, you're likely not hitting the right recipe.
To get coffee shop type lattes at home, you need a real espresso machine. A single boiler unit with a steam wand will do the trick, but nothing short of one will.