Definitely introduce formula: a fed baby is a happy baby! No matter what you give (formula or breastmilk)! Here is a comparison table with the best formula that mimic milk the best.
If your baby has hard time latching and extracting the milk learn about proper latching.
At the same time if you introduce bottle through pumping or with formula, use Premie nipple so you won’t create nipple confusion. Read more How To Avoid Nipple Or Bottle Rejection?.
When you give formula, pump at the same time! The more you pump the more you increase your supply!
In addition read more on increasing milk supply