Ah, lots of useful info here
The most important thing in your post is that your baby is fine and thriving. This shows more than anything else that you do not need to be concerned about your milk supply.
It is normal not to have milk overflow/dripping. This is something that almost every mother finds ceases as her baby gets older. Expressing only shows you how much a pump can get out at that particular moment. The baby removes milk differently and often more efficiently - sometimes, it's true, pumps get more out than the baby eg when a baby is small, weak, pre-term. In your case, this doesn't apply. It's very common for expressing to produce less with very established breastfeeding - does not mean the baby is getting less.
Expressing does not lessen your supply, no, but it is pointless doing it to judge your supply - hope I have convinced you of that
Just feed direct, and if you are sore, you can see someone who knows what to look for and get things fixed, often by amending the way the baby akes the breast.
Nothing you have said makes it sound like you need formula - not one word