Amtrak has 2 trains from So. FL to NYC: the Silver Meteor in the morning, and the Silver Star midday. But the Silver Meteor is currently suspended due to staffing shortages related to the pandemic.
The only time you can make a connection to Boston from the Star is if you depart FL on Saturday, arriving in Boston at 1:15am Monday morning. For the rest of the week, there is no train to Boston departing NY Penn Station late enough to make a connection, and you would have to stay overnight in either Washington DC or NYC to get a train to Boston the following day.
You can't specifically reserve a VL II, but you can request a specific car number when booking on the phone (but not online.) Currently, the Star is running with combined equipment from both the Meteor & the Star, including 5 sleepers for the past couple of weeks. As
@jis said, on the combined Star, Sleeper cars no. 10, 12, and 14 have been VL II's, but there's no guarantee.
As of now, Amtrak's booking engine has the Meteor resuming on Monday, May 23, but of course that could change. If you choose to wait until the Meteor resumes service, know that prior to the pandemic, the Meteor usually ran with 3 sleepers, and cars 10 & 12 were usually VL II's.
There was also an overnight train at 10pm from Washington to Boston which is currently suspended, and also scheduled to resume on May 23. So after it resumes, if you would prefer to ride the Star, you could get off at Washington and wait 6 hours for the overnight train to Boston. The pre-pandemic Star usually had 2 sleepers, with car 11 being the VL II. The overnight from Washington to Boston had a single VL I sleeper. Amtrak's booking engine does not offer this connection, so you would have to book it on the phone, or you could try booking it online as a "Multi-City Ticket".
Remember that train consists and, especially, resumption dates for suspended services are highly subject to change.