Well...I perfectly understand your wife as I just adore wine tourism in Italy.
The macro clusters for wines in Tuscany are Bolgheri, Chianti and Brunello/Rosso di Montalcino.
Booking is obligatory if you want a nice tour with explanation rather then pouring a sip of wine in your glass and then whatever.
Over the last years tasting is not free of charge any more, the pricing I see is around 25 euro for 1h30min tour with some basic wines. Some very small producers which are not tailored for massive wine tourism still do it for free.

You are mentioning travelling by train - you would need a car to get to the wineries.