Surzhik is not a variant of some language - ukrainian or russian - this is just a mix both of it.
Just like Ukrainian computer slang is neither Ukrainian nor English but some new language
Actually, Surzhik is a spoken variant of Ukrainian with a great (mostly lexical) influence of Russian. Not Russian with Ukrainian influence, not random mix of them both. Some Russian words never appear in Surzhik. Russian influence is mostly lexical (and the one who learned literary Ukrainian after Surzhik speaks Ukrainian with no accent, not like Russian native-speakers).
So the right way to learn literary Ukrainian after Surzhik is step-by-step replacing borrowed lexicon with literary words and correcting grammar sometimes.
py -3 -m pip install git+https://github.com/snoack/python-goto