You can also measure the work output directly which is not hard in most industries.

I don't work in an IT shop, but we have no issue seeing who is slacking and who is actually working when working from home just from the deliveries, no monitoring required. But I guess that's included in your "other proof of work".

There are some people who need discipline though, there were some guys in my previous company that were notorious for showing up at the 10 am teams meeting with a bed head and a yawn or the 2pm meeting outside in their garden. You could also notice their output go down quite drastically.