What is the correct return ticket duration for applying for a TR visa in Thailand with a 30-day extension?

I'm looking at same for around Xmas..60 day then 30 day extension ...but would be booking flights for 90 days even though extension isn't done.....Also not sure ?

Italians do not qualify for visa on arrival.

Italians can get visa Exempt. If you arrive before April 1st you'll be stamped in for 45 days, or if arrival is after this, you'll receive 30 days.

Both of these can be extended for another 30 days at immigration.

You'd need to ask your embassy what kind of proof they want for tourist visa application. Generally if they want to see your flight then it will be 60 days they are looking for.

Also your airline may require you to show proof of leaving Thailand within 60 days if you fly on a tourist visa, or proof of leaving within days if you're flying without a visa.