Posted in r/TheWayWeWere is this photo from the 1940s of a wearable cow-milker's stool:

It's a brilliant design. You can sit or stand without having to put the buckets down and grab the stool. Also, they're one-legged not only to save weight, in the case of this wearable variant, but because' it's appropriate for the task, for safety's sake. As one commenter pointed out:

"I went on a field trip to a farm and they showed us this one legged cow milking seat. The farmer told us that a seat like this was great in case the cow fell over or for some reason started walking sideways onto the person milking it. All the person had to do is spin 180 degrees and could quickly stand up and move away, taking the seat with them (tied to them), possibly avoiding injury from the cow tipping over, or stomping on them. As well as leaving the ground clear for the cow's safety."

One-legged milking stools are still sold today; this one carried by Lehman's goes for $30. (It doesn't, however, appear to have the cutout for the waist strap.)