Hi there sweetie40,
I can't comment on the skiing as I don't ski, but I have had massive problems with costo over a number of years. Thing is the best thing for it to decrease the inflammation is to avoid activities that cause and and therefore exacerbate the costo. Skiing would I believe definitely be a no-no as the pulling and stretching across the chest would become intolerable. Deep breathing could also put strain on the chest muscles and cause a lot of pain and in the conditons you would be skiing in then deep breathing I would expect is par for the course..
Some people find that applying hot packs to the chest can be helpful in relieving symptoms. They are best applied several times each day, especially before activities that may irritate your symptoms. While ice application can sometimes help with most conditions of inflammation, applying ice to the chest can be quite uncomfortable. The one thing that is good for it is to rest.
I personally have a lot of problems with costo as it is caused in my case by another illness and also exacerbated with having open heart surgery. So I am almost always very tender in that area with inflammation. I have steroid injections into my chest every 3-4 months. Whilst initially it is a bit painful when having the jabs, for me the relief I get is worth it.
If you have been given a firm diagnosis of costo then your doctor should have advised you of these things. Very difficult I know when you are going on a skiing holiday, but I think you will be in so much pain - I certainly hope things work out for you.
PLease take care