I forgot exactly but it was like 2-3, max 4 documents, easily obtainable here - certified copy of the passport, proof that you still run  the business and forgot what else ... either proof of residency or statement from the bank that you have funds, maybe health insurance... but now health insurance comes with the residency.... it was trivial and last I remember - it's been a while since I owned a business - the tax was in ballpark of  60-70 EUR ... possibly higher now.
Just  make sure to start the procedure at least a month before expiry just in case...