Less sea ice also exposes the polar winter atmosphere to warmth from the underlying ocean. In some ways, yes. Permafrost is melting in Alaska and in Siberia. Northern residents provide anecdotal corroboration, sometimes sighting fish, birds and insects not native to the Arctic. With the advent of satellites, we can be more precise for the period 1978 to present.
Thickness is much harder to measure over the expanse of the Arctic Ocean.
Some information about thickness can be obtained from nuclear submarines which use upward sonar to measure ice draft. During the 1990's the US Navy provided submarines for scientific study of the Arctic. Results from cruises in the 1990's can be compared with declassified data from military missions from 1958 through the 1970's. Tracks in blue are from 1990's scientific cruises. Tracks in red are from earlier military missions.