Yubikey keys - zero difficulty adding multiple - if a site doesn't allow multiple I wouldn't lock my account down to a single point of failure. All the big players seem to offer it, and I can not recall any that didn't. Google in the "advanced protection" days forced you to have more than 2 keys for this reason.
By count of sites, most sites don't appear to take security that seriously so anything more than a password is off the cards, but the big ones - the ones that actually matter; email, cloud, etc. should all be able to be secured.
By count of sites, most sites don't appear to take security that seriously so anything more than a password is off the cards, but the big ones - the ones that actually matter; email, cloud, etc. should all be able to be secured.