I give DD expressed breast milk and try to give her a bottle every couple of days so she stays used to it. She uses a Medela Calma teat and a regular bog-standard Medela teat. She has also used Avent newborn but I think she found this one hard work. Here are my tips:
Have a range of teats to try.
Give a bottle a few gos with you (and your boobs) on standby before you need to be away.
Make DH/DP/someone other than you give the bottles. Make sure the bottle giver is going to be calm and persistent.
Try the bottle when your baby is hungry but not starving, perhaps two hours after the last feed.
If baby is in a real strop and crying etc, my DP did a good trick of a bit of finger sucking/cuddling to calm DD down, then just slipping the bottle in in place of the finger.
Don't panic in relation to mls (amount) of milk drunk from the bottle. I think, and am no expert at this, that people go for 100-120ml for one feed, but if your baby takes only say, 70-80ml in one feed, I think that's fine - it may be that they're less hungry / your milk is more calorific, and it's only 7 hours that you're away.