What do you mean about Chelsea Piers? They have 2 rinks, a lot of hockey time but also a lot of freestyles. Publics are generally crowded but if you go at 1:30 to the days that have that start time for a public the session could start out not too crowded unless there's a group which is really hit or (totally) miss as they can be large.
Not sure who said Bryant Park is huge - it is very crowded and very small and they generally don't let you do any figure skating but that could depend on the staff that day. They're not supposed to let you go backwards (same with Wollman). They might have meant Wollman, which is very big but oddly shaped (more like a baseball diamond). They have morning freestyles though and some adult classes some mornings that should be good.
I thought Wollman and Rock Center were open until first week of April but I could be wrong. I don't skate at either. Rock Center is crowded and not too big. Hit or miss but I think you can go really late at night and usually looks empty uber late (when the news cuts to it).
There are a bunch of other really small rinks in the city, probably not worth it.
If you want to journey out of the city, Prospect Park for outdoors is supposed to be decent and not crowded during the day during the week. They have a couple of restyles too. Easy subway ride outside the city to Brooklyn and in Prospect Park.