Oh piglet, you sound hurt by your experiences with Katie. I'm sorry. Some women find it easy but for most it takes persistence, hard work and some stubborness. It's a new thing for you and the baby to get your heads round and you both have to learn how to do it. You absolutely need support around you. Proper support from breastfeeding counsellors, midwives or hvs and support from family and friends. Not seeing how much is going in is a common concern. You have to be led by the baby. You latch as often as possible at first and let their health and well being be your guide. Lots of wees, poos and an alert baby who gains weight are the best signs that the baby is getting enough.
Once bfing is established in the first weeks you can express and introduce a bottle or a cup (they lap like a cat!) and you can get some rest while somebody else feeds. Some women find they cannot express though but there's nothing to say you can't give the odd bottle of formula if you want or need to.
Don't be afraid next time to ask for help of the sort you need. Those first few weeks should be about taking it easy, putting the baby to the breast, encouraging lots and lots of skin to skin contact and feeling supported.
You have MN too now . It saw me through some bleak times. I don't mind admitting that there are several MNers who made my bfing success what it is. You can ask for help on here at any time of the day and night, formula help, breastmilk help, cheer me up I'm bored help. It would be nice to carbon copy such good support into other quarters sometimes.
Kudos for considering having another. I'm still in shock from the first birth.
How old is your little girl?