Travel abroad is not explicitly banned under the Tier system but if there is no travel corridor in place (and very few remain) then you are travelling against FCDO advice. Most policies will not cover you in this event unless you go to a specialist. If you do, ensure it covers you for mountain rescue and winter sports.
The rates are still very high in many winter sports areas so I cannot see travel corridors being back for some time.
Even if there is no quarantine on arrival at your skiing destination, if no travel corridor, there will be 14 days on return. This might just be ok at Xmas and Easter but you have to take a view on children missing school after half term (unless something changes by then which seems unlikely). Also the risk you develop symptoms and have to quarantine when at your destination, or cases surge and local restrictions apply.
Soon, you should be able to test out of quarantine after 5 days under the proposed new regime. This will cost 100-120pp. Skiing is expensive anyway, so I'm not keen to incur extra charges.
We've been told that some European ski countries may adopt pre flight testing as a prerequisite (I believe Italy, Greece already have this in place). That's another 100-120pp if your destination decides you need a negative test to go there.
Track and trace (particularly in the school environment) can throw up surprising results. You may not think someone is a close contact of you or your child but your personal view is not determinative! You may choose to stay home, pull kids out of school, and ignore the phone having booked 2 days before, but that's not "back to normal" is it? Also councils are now checking up on people meant to be self isolating and the fines are hefty.
Anyone may accept these risks, be lucky and get their ski holiday and none of this happens, but my point is that we are a long way from back to normal. The middle of Jan is when the French government will hopefully allow the ski lifts to open. It doesn't mitigate the risks of all the above unless something else changes. And the best estimate of us getting back to normal according to ministers and scientists is spring/Easter when the vaccine rollout is well underway.