I do love a good ice bath after sauna, haven’t had one for years sadly.
A friend of mine did something similar, whole body (except head) ice bath, “Wim-Hof-Methode”.
I went (not ice) swimming beginning of April, in a lake, there the friend I went into with recommended keeping the hands out of water. That helped a little.
For me, easiest way to get in is just… go. Don’t stop.