I've found gro bags good for restricting leg movement, and settling, but obviously they don't restrict arms.
There's a postal sling library, "It's a sling thing", so you can try a few without having to pack up the kids and actually get to a meeting, where people may ask questions, etc. Our local sling library also does postal loans.
We do need more therapeutic foster carers, but then society would have to decide to 1. pay for the training needed, and 2. pay these highly trained people adequately. I know that there are some who post here who are highly trained foster carers, who do it for love not money, but generally if if need people to be highly trained, doing a difficult job, then that needs to be well remunerated. And fostering allowances just aren't enough.
Plus, there is the huge pull of familial ties for this OP. I think the last thing she may need to hear is that a foster carer could do this better, that's like telling a mum struggling with a newborn that a trained nanny could do it better- probably true in the short term, but long term outcomes, it's better for that new mum to be given help, just as here that if OP can manage this, then it could be rewarding all round. OP, that's not to say that if you make the decision you can't manage this, then that's not the right decision, too. My impression from your post, though, is that you really want to find a way for this to work, in which case that does sound like long term a good plan, but just now sounds like hell for you. If you feel you can do this, then it'll be so much better than foster care, no matter how trained the foster carers. If you can't do it, then you can't do it, and foster care will be ok, because they will be trained, although at this young age, adoption could be a possibility, and they potentially wouldn't be more trained than you are.
This was the first hit on google for swaddling, which is interesting: pediatrics.aappublications.org/content/early/2016/05/05/peds.2015-3275 but it's a very small 'meta analysis' given only 4 studies met their inclusion criteria! Like anything, it'll be a risk assessment- what's riskier, swaddling or weighed blankets etc, or you falling asleep exhausted with her in your arms in an unsafe place/position? Or not being able to parent? Is co-sleeping an option, to get you some sleep at night? Again, it's all a risk assessment, co-sleeping has risks, but so does parental exhaustion, and the benefits to attachment.
OP, I really feel for you. I definitely think SS need to be offering much, much more support. I think health visitors sometimes have access to free nursery time for your 2 year old, if that would help give you some space with the baby? I understand you want time with the 2 year old, too, though! Time will help get everything clearer and easier. A threat of breakdown may well get SS more engaged, as they should be.