According to Thai law, when you transfer money to buy property, the transfer must be made in your country’s currency, in your case euros, and not converted to Thai baht first. The Thai bank will then convert the amount to baht after receiving the money in euros. So, don’t let your bank convert to baht, keep it in euros. The reason for the transfer should be “Purchase of condo”.
Thai banks seem to use a reasonable exchange rate. This worked out well for me when I bought my condo, as the rate used by the Thai bank was way better than the rate an Australian bank would have used if I’d converted $A to baht before doing the transfer.