I don't think any airports have lockers anymore because of the security issue.

There's a Courtyard at Flora which is just steps off of the green metro line (that one that meets the airport bus at Dejvicka).

I like local hotels better, like the Orion and the Anna, which are a couple blocks from Nam. Miru metro stop (also on green line).

IF you want to stay more in the center, hotel Liberty is right next to Mustek (also green line) as is Hotel Friday. Hotel Hoffmeister is both next to Malostranska stop and right under the castle.

I know Orion and Anna, they are both nice local style hotels. Not familiar with the others aside from location....check tripadvisor.