I'm finding this to be the case as well. You're trying to detect complex patterns that can take a good week to suss out and influence, and yet which are changing on approximately that same timeframe. You're continually behind the bus.
The way our child behaves/reacts with me is very different to how he is with his mother. For example when our child won't sleep at nap-time, or in the evening, I put him in a pram and take him for a walk around the block. It's a horrid solution, but it works about 90% of the time.
When my wife has tried this it has never. once. worked.
(He plays differently with the pair of us, and tries different behaviour. It is kinda fascinating to see the difference - part of that is our relative strictness, but part of it is him I think.)
My wife always had problems with nap time when they're a bit older 1½-2. But for me it was a process, starting at lunch, moving through story time, then I'd maybe sing or hum snuggled next to them on the bed.
She'd do lunch, then play, then read a story in a really animated way, then try and put them down for a nap and wonder why it wasn't working.
A sling is good, ambulatory frequency, close to heart, they feel your breathing, are warm but heat is regulated by the parents body too.
As for slings I ruled them out early on - Finnish winters mean that babies, children and parents all need to be pretty warmly wrapped up. That made slings way, way too bulky and impractical.