Learn Italian: Sbadiglio perché ho dormito pochissimo. - I am yawning because I slept very little.

Here, pochissimo is used as an adverb modifying the verb ho dormito (I slept). Adverbs are invariable, meaning their endings never change to match gender or number. Even if the speaker were female, it remains pochissimo. While poco can act as an adjective (like in poche mele for 'few apples'), when used to describe a verb, it stays fixed in the masculine singular form.

How does the absolute superlative (adding -issimo) work for words like poco?

Some words like poco, molto, tanto, and troppo are adjectives that can be used directly as adverbs without adding an -mente suffix. To emphasize them and say 'very, very little' or 'very, very much', you just drop the final vowel and add -issimo, exactly as you would for a regular adjective.

Why is there an h in pochissimo when there isn't one in poco?

In Italian, the letter c followed by o (as in poco) makes a hard 'k' sound. If we just added -issimo, the c would be followed by an i, creating a soft 'ch' sound (like in 'cheese'). To preserve the original hard 'k' sound of the root word, we have to insert an h, resulting in pochissimo.