A few weeks ago, I would normally immerse myself in a light novel during lunch breaks, but these days, I'm just toso snowed under with my studies that the only things I crave is some sleep.

“So… that…” is the correct wording. You could also write “too… to…” but you would have to follow “to” with whatever it is that you cannot do.
“Only things” is plural, while you only named one such thing.

So, all my spare time would beis devoted to taking a quick naps, or hechar una siesta as I like to call it.

Unless you only have one single chunk of time in which you are free, the plural “naps” makes more sense.