I'd ask a slightly different question. Do you really need to spend 80K immediately on the house straight away? Personally I would avoid taking on even more debt after borrowing E368K to buy it, if at all possible - you haven't given any indication of how this would impact your ability to repay it, if its no issue or if you would be squeezed etc.
Is this extra money required to do *everything* that is needed upfront? Is it liveable currently? Could you live there as it as doing maybe E20K worth of work that is really needed. Taking a moratorium of 6 months at the start of the mortgage and/or borrowing another 45K will cost you quite a bit in interest over the term.
I'm not sure which of the two options you provide would be better, as you haven't said your mortgage rate, or if its fixed, LTV etc. A quick Google tells me that home improvement loans run at about 7%, so it would seem to me that a top up on mortgage would probably be cheaper than getting separate loan, assuming your current mortgage is around 3%.
However, for me doing neither of those would be my preference!