fate I have a question re the "firm hand" as I really believe in teaching independent sleeping - how do you do this with a baby that wants to move at all costs?
Well really, they don't want to move "at all costs". Because it's impossible to go to sleep while jumping around and baby cannot survive without actually sleeping. So while I appreciate (and have said above) that this is a bloody nightmare of a phase (I'd put pulling yo standing as the very hardest work time, in terms of sleep. Second is rickibg on all-fours pre crawling).
So it begins with knowing that you, as parent and adult, do know that the child needs to learn to still. That involves multiple ways to teach, the "firm hand" is just one of. The firm hand mostly comes at the end, once you have convinced child to lie down and you are just reaffirming that and aiming to still limbs rather than whole body.
Before that there are things like multiple lie-back-downs. Anything that isn't lying down would result in me lifting baby and immediately lying back down (as I would and have done from birth, so no battle in doing this).
My settling method from newborn has always been lie baby in cot, lie down myself on bed next to baby, dummy in, hand on chest, wait for baby to go to sleep, remove hand and put dummy aside, leave.
So through this hyper mobile stage, it is just a return to this. With loads of repetition. I would repeatedly not accept anything other than lying down and any lying down is "rewarded" with my hand on chest for reassurance, as has always been.
Any attempt to get up and I'd lift baby up about 30cm or so (just off the mattress, not in my arms) and start again. Repeat a million times over.
The key message I would be getting across is "the cot is for being still, calm, quiet and relaxed only. Nothing else happens in the cot". So just repeat until this happens. This phase is only usually a few weeks, mine have always mostly got it within a week.
Once mine 'get' that there is no other option but lying down and stop fighting it, I may get some massive leg kicking instead (common in the earlier pre-crawling phase). I would still this with my other hand on legs. Again, reiterating that the cot is for going to sleep only. And to go to sleep means being still, so there's zero tolerance on not being still.
As an aside, its worth mentioning to the attachment parents that this phase is possibly easier to get through by use of "full body cuddles" ie, you use your whole body wrapped around baby while cosleeping to keep baby still when going to sleep.
I would often utilise full body cuddles and cosleeping for the odd daytime nap through this stage - given bedtimes become harder work so I often couldn't be bothered to deal with it for naps too so we just napped together instead.