curls I used to give Gaviscon in water (boiled, cooled obviously) in a bottle. LC took it fine like that, then I would BF as normal. I did start out killing me nips with expressing to mix it up with but quickly found the water route worked fine. It was only a very minimal amount of water so didn't interfere with his BM intake and he was fine going between bottles and the breast.
My feelings on whether you should move to formula are that the only person who knows how you feel health-wise is you. If you wish to continue to give her BM and you are ok with your pain level, do so. If staying off the meds is going to cause you problems which can't be reversed, maybe its time to move away from the BM. Noone else can make the decision and in the end you've done the very most important part - the initial few weeks - and while clearly breastmilk is "better for babies" than formula because it's got more good things in it, formula is bloody good stuff and will grow her well and healthy.
Formula has all the nutritional requirements that the Squeaky One will need and although it doesn't have the additional anti-nasties stuff, you've given her loads of that already which is brilliant, and that won't go away - and babies who are 100% FF from birth are absolutely fine. Whatever decision you make, always feel positive about it as it will be the right one for you and your circumstances. There's nothing to "feel guilty" about - quite the opposite. You didn't ask to have this horrible thing going on with your body and more important than BM is your own health and the ability to look after your little girl properly with a healthy bod.
But in the end, only you can make the decision because it's your body, and you know how well it's holding up.
Regarding Motherease, they shouldn't be soaked through that quickly although some babies are just "heavy wetters"... Actualy being wet isn't a problem for most babies, and won't do their skin any harm (disposables feel drier but the urine is still there and you have additional chemicals which can irritate the skin, too). If they've pooed in the nappy it will interact with the urine and this isn't a good thing, but again it's the same with sposies.
OK, so she's soaking through them in 1-2 hours? Wow. And you're using the popper-in booster? Isn't it huge on her with the booster? You can't fold them down, can you, with the booster in? You could try using a bamboo booster instead, or as well as, the popper-in one which will be much more absorbant. Normally I'd expect a nappy like that to be soaked through as you describe in 2-4 hours.
I don't bother with paper liners although if you go onto formula you may need them as the poo changes. I use fleece liners and just pop them in the wash with the nappies. Much less faff and softer on the skin, too. While she's fully BF you could just not bother with any liner at all.
You're not using any fabric softener in the wash are you? It can really reduce absorbancy but surely not that much...
ski you are being incredibly committed continuing to express. Any idea why they're not doing their job? Is Bear cluster feeding at night/fussy at night? I know you needed to start with FF because he wasn't getting enough at some point in the day (wasn't it the evening?) but I wondered if the bottles had stopped both the upset from not getting enough milk, AND clustering?
Apparently African babies who are carried all the time and have full access to the breast (and feed several times an HOUR! ) don't fuss/cluster feed in the evenings. So maybe that's the option - be permanently boobs-out .