Well, I envy your financial responsibility.

However, if you're not going to spend real money in the game, I'd strongly recommend you continue to do 11-pulls, at least until you get more solid 5*s. You'll have bad luck with some of them, even most of them, but you have no other way to even have a chance of getting new quality 5* or even 6* girls on your squad.

I've probably went through about a dozen premium 11-rolls with the awful 5* and 6* odds (a few of them I purchased, most of them just through collecting FGs) since I joined and I have gotten two 6*s and at least ten 5*s that way. It's tempting to get down on the 11-rolls when you get unlucky, but it's worth noting that the odds are objectively over 50% with every 11-roll that you'll get at least one 5*. In other words, based simply on the numbers an 11-roll will more likely than not (not always, but probably) give you at least one 5* character that will probably be considerably better than the 'free' 5*s you'll earn through events.

And I'd say that's worth more than stamina rejuvenation if that's the only way you can potentially collect more quality 5* and 6* girls.