My cats get dragged kicking and howling off to the vet for the Program injection every 6 months.
The Program injection works like birth control for fleas and stops them reproducing. I have indoor/outdoor cats and it really does seem to work well - certainly we've not seen a flea since the cats have been having their twice-yearly injections.
It is a bit more expensive than drops on the neck, but not prohibitively so. I rate it not just because it works, but because I don't have to wrestle with peevish cats who don't want stinky drops on their necks and are willing to fight me about it. With the injections the vet is the one risking his fingers 
I don't think every vet does Program, but I found it worth the bother of ringing around for one who did.
Hoovering every other day is good. Are you really getting into all the little nooks and crannies? Along by skirting boards and close in around the edges of furniture? Down behind the sofa cushions? Emptying the hoover immediately after you're done so the fleas don't just hop out and start annoying you all over again?
Have you also got into the habit of regularly hot washing blankets, bath mats, pet bedding etc?
You're probably doing all of the above anyway, but thought I'd mention it just in case.
I hope you get rid of the little fuckers soon.