"Jij bent klein, net zoals een muis."
Translation:You are small, just like a mouse.
Both are fine. 'Je' is the unstressed form of 'jij', which means that the emphasis in the sentence is on an other word than 'je'.
Why is it spelled "klein" and not "klijn"? Sounds very similar to other "ij" words.
Because words that are spelled with ij originally had a long i sound. However, that changed to a ei sound and hence ei and ij sound the same. On the other hand words that sound the same can have a different meaning depending on if it is spelled with ei or ij.
Net zoals - are these words always said together to translate as ,just like, or dose 'net' mean just and 'zoals' mean like.