IAGTBF, I've been where you are with the nightmare boob situation and had mastitis by day 8 with my DD. God, I feel for you hun
Ok, first thing, are you using Lansinoh lanolin cream for your nipples? This stuff saved me. It is incredibly healing and you can get it from Mothercare and probably chemists too. Use it after every single feed and it is pure so baby can get it in their mouth without harm.
Also you can take regular paracetamol as well as ibuprofen so keep the pain under control as much as you can, it's exhausting on it's own.
Right, boob health out of the way about the bottle business....
We used Tommee Tippee 'closer to nature' bottles to combine feed DD and never had any problems at all. This was with EBM and also formula. The teat shape is very wide at the base and was fine for our LO.
Incidently, not to stir up a nest of hornets , but we also gave our DD a dummy from day one , as I had no idea that this is not advised with BF babies and she had not a hint of nipple confusion. She loved her dummy and she fed like a demon from breast or bottle. So from my vast experience of one child, now 10 months, I am not sure I believe much in nipple confusion.
Annyy-waaayyy......The only bug bear with these bottles is that the numbers on the side are very hard to see but unless you have especially poor vision, live-able with. It shouldn't concern you too much anyway with BM as you wouldn't usually know how much your baby is getting anyway. If you begin to use formula at all in the future that will be when you notice it.
The only thing I would like to say, is that we introduced the bottle of EBM much later than you are (I wish I had done it sooner but I was completely bonkers very committed to feeding DD myself (in spite of being in agony, shattered etc...). Don't make my mistake and persevere with the expressing (or formula if you choose to) and share the feeding with your DP, mum whoever you've got. I know you need to do it for your baby's weight, heath etc at the moment, but longer term, it will help you get some rest and preserve your sanity too.
Lastly, my friend's BF baby is also 1 week old today and she is already expressing and sharing feeding with her DP (sensible lady). I shall ask her which bottles she is using and post her answer on here a bit later as her experience is even more relevant to you than mine.
HTH, and good luck for your baby's weight gain and your boob health too!
lots of love MOLM x