Two routes, and which one Thailand takes
An apostille is a one-page certificate that closes the question of whether a signature is real, and member countries accept it without further steps. Consular legalisation answers the same question the slow way, with an Italian stamp followed by one from the destination's mission. Thailand still works on the slow way, and will until the Convention starts running there.
Thailand's accession and the 2027 date
Thailand has joined the Convention, but joining is a paperwork event and the practical change comes later. It comes on 28 February 2027. A file that has to be read in Thailand before that morning follows the consular chain in full. A file used afterwards needs one certificate and no consular visit. Planning around that line is the whole trick on this corridor.
The Naples to Thailand route step by step
Order or refresh the record first, then match it to the right Italian office: the Prefettura in Naples for administrative papers, the Procura della Repubblica for deeds and court output. Pay the €16 stamp where it is due. Hand the legalised bundle to Thailand's consular office in Italy, which signs last and seals the set for travel.
Why a Thai pack moves slowly
Visa, marriage and work packs for Thailand tend to move as a group rather than a single sheet, so the chain runs several times in parallel. That is where the cost of the consular leg is felt, because each document is charged and queued on its own. Sending them together is the only real lever on the timing you have.