I'm confused between what Oyster can do, and what it will do.

I travel regularly but infrequently, so my pattern may be a Z1-6 daily
travelcard 4-5 days a month (though I've never worked out if it's
cheaper to buy anything else, if I leave early, I sometimes buy a Z6 -
1 single and then a Z1-6 travel card after 9.30 for my next trip). I'll
also perhaps buy a couple of returns inside Z6 or Z5 & 6 on a weekend.

It's not worth my while buying a monthly or weekly pass, so I think that
makes me a prime candidate for an Oyster Prepay. I'd like to be able to
load up a card with £100 and just tap the gate on entry to a station.
If I make two journeys I'd be charged two lots of Singles, if I make a
third, I'd like the Oyster card to make itself into a Travelcard.

Am I dreaming?