Sorry to hear you're having a difficult time atm.
From what you've said your LO is clearly not hungry but has learned nursing is how to fall to sleep, now you are teaching her there is another way to fall to sleep so there will be some resistance and frustration on her side, after all she is tired and all she wants is to slope off to dreamland (the way she knows how to, but even that is frustrating her because she is full). It's understandable there might be frustration for you too because you are also learning a new skill, a different way to help her to sleep. You will learn it together and you WILL get through it. Stick it out it is worth it.
Your LO is already showing the ability to go to sleep and transition from one cycle to another without nursing, she does this when you return to her after the 5 min sleep to do shush pat, and she is transitioning at night so you are already on the right road.
I'll try to answer a few of your concerns:
I wouldn't bother with the paci. If she rarely takes it anyway I don't see much point in encouraging it at this stage. My LO always refused a paci so I had to find other ways to sooth him, in the long run I'm happy it went that way as I had one less thing to wean later on.
Shush/pat is not the same sort of prop as nursing. For one thing nursing isn't always working for you now as she is full and yet still trying to feed to sleep. Shush/pat can be gradually reduced (relatively easily) as she gains independence where as nursing is either on the breast or off the breast, there is really no in between. Shush/pat can be continued in the cot which I doubt you can manage with nursing. Shush/pat will still be available after you stop breast feeding and can also be carried out by another care-giver such as DP. Unless you're planning on breast feeding throughout toddler-hood you really do need to wean the feed to sleep prop.
I know at times it feels awful when your LO is crying and you feel you are withholding her comfort, but you are teaching her, giving her the gift of independent sleep and you are certainly not abandoning her, this is not CIO at all, you are with her, comforting and soothing her throughout the whole process. Always letting her know that you are there for her. If you like talk to her a little, tell her you know she is tired but it's ok to be tired because it's nap time and you are going to stay with her until she reaches dreamland (or just tell yourself this, sometimes you need to reassure yourself that this is the right thing).
Sucking on your shirt sleeve might not be such a bad idea in a way. It's ok for her to have a lovey and for you to introduce one if she doesn't already have one (they usually choose their own but I influenced my LO's lovey attachment by holding it by him through every feed and falling to sleep). A lovely is something she controls herself (unlike a prop which is controlled by you). My DS uses a muslin square as his lovey (always in plentiful supply and can easily be washed/replaced) and will hold it, rub it on his face and sometimes suck on it for comfort. Your LO might like something like this, an old shirt of yours perhaps or a toy with a label (they love labels!). DS usually find the label on his muslin and gives it some extra attention, he finds it very soothing.
The 5 min nap. You can try httj (holding through the jolts) as it could well be this that's waking her. Position yourself so you can hold her quite firmly as she jolts in her sleep (even with the swaddle) and if she wakes shush pat straight away.
When holding and cuddling and shush patting do try to get her down to the mattress before she is asleep but continue to shush pat and sooth her in the cot. If you stay with her until she is in a deep sleep, it teaches her how to fall to sleep on the mattress which is a very different feeling to being in your arms, when she opens and closes her eyes what she sees will begin to become familiar because she is seeing the room from the right angle. As time goes on you will be able to reduce your shush pat, honestly you will. And yes, one day you will take her to bed give her a lovely cuddle lay her down, say goodnight and walk out of the room. It really does happen.
Can you post your EASY so we can see how your day looks? It could be that she is perhaps UT at nap time and this could be adding to the difficulty of getting her to the sleepy state. If she is good and tired (but not OT) and you have a consistent wind down you will be paving the way towards sleep and will find the shush pat method more successful.
