How to introduce formula feeding whilst breast feeding

[SanchP]

Hi my LO is 4.5weeks old I've been expressing and giving her a bottle since 2 weeks and haven't had any issues with nipple confusion. The last four days mainly in the evenings and night time she feeds on and off for an hour then gets really angry with me won't latch but still shows signs of hunger biting her hand and mouthing my arm. I'm thinking of introducing formula as I'm struggling. Has anyone done this?and how should I go about it?
Many thanks

If she refuses formula alone at first, you can try mixing it with some pumped breast milk to help her get used to the taste. Mix the formula first, separate from the breast milk. Once the concentrated liquid or powdered formula is prepared, it can then be added to a bottle of breast milk or given after the bottle of breast milk. NEVER add undiluted powdered infant formula or concentrated liquid formula directly into your breast milk, and you should NEVER use your breast milk in place of water to mix concentrated or powdered infant formula.
She might need to go longer between feedings. That's because babies don't digest formula as quickly as they digest breast milk, so they're likely to feel full longer. It might mean you produce less milk.
Be warned, her nappies will be different. It will be firmer (about the consistency of peanut butter), be tan or brown in colour, and smell stronger. It will probably be less frequent too.