Based on your preferred features, you seemed to be against coinhive's terms and conditions.
Or you still haven't heard of coinhive's API?
I've seen some ETN pool websites that offers slightly the same features, but I can't remember the link.
There seems to be a performance issues with in-browser mining aside from slower output like the miner stays "Mining" even after hitting stop/pause button. Something simple enough to fix for a good web developer.
This wasn't much of a help but I hope this gave you an hint on where to search.
I tried finding scripts like that with coinhive. But no matter how much I look, all that comes up is how to make your users mine for you... But I don't want any profit myself.
Performance doesn't matter a whole lot to me. This is mostly for show. Just making a MLM sort of website (Multi Level Marketing), basically a legal pyramid scheme where people pay a monthly subscription, but to make it "legal" I want to offer multiple services to those users if they have a tough time to "invite" other users.