Having frozen addresses with funds try (!) command in the amount section of the Send tab.
Thanks for the quick reply.
Just tried it, it fills in the max non-frozen amount it seems.
It's useful, but not exactly what I was hoping for: I guess I'm increasingly using Bitcoin (and with it: Electrum) like I would use a bank account, paying for services, moving between exchanges, etc.
I would be nice if I could see, at a glance, my total non-frozen funds, which are the ones that are really available to me.
But I also can see that there's probably more important stuff to implement than display tweaks like that.