Hi Roni, it sounds like you just need to cover your starter a little more securely so that it doesn't dry out on top. The reason we say to "cover loosely" isn't because the starter needs airflow in order to ferment properly (it doesn't), but because fermentation gases can build up in a tightly lidded jar and cause the top to pop off. As long as you leave sufficient room above the starter level for fermentation gases to collect, and remove the lid now and then, it's fine to use a lid or cover your starter securely with plastic wrap. 

Your starter is likely to take a bit longer to ferment when stored at 68-69F, but it should still work. If you can find a slightly warmer spot (70-80F) this might cause things to happen a bit faster, but I wouldn't recommend going over 80F. Your oven with the light on may be fine, as long as you cover the starter a bit more carefully so it doesn't dry out on the surface. 

Barb

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