(Hello - it was brought to my attention that you asked for Sigana - which unfortunately I can't find in Tuscany. I had assumed that you had misspelled the name of the town and were looking for Signa - which is very similar in the spelling. If you want to send me a link to the accommodations, then I can be more precise in assisting you.)
Try looking at the trains - there are frequent runs from the airport which last about 1 hr 15 min leaving you in Signa. You will have to change trains, first you catch the people mover from the airport to the city center and then a connecting train to Lastra a Signa.
Check with your accommodations on how close the train station is, and if they can arrange for a taxi to pick you up.