I come across those kind of jobs from time to time.
The key is to NOT bridge the gap between the skirting and flooring. If you do, the expansion in the flooring will pull the caulk/etc away from the skirting.
Depending on the size of the gap, I run two layers of 1000 grade lining paper under the skirting. If the skirting is a reversible skirting, I use minimal expanding foam to create something for the filler to stick to. I cut away the excess foam and then use something like Toupret RedLite to fill down to the floor. Once that has cured, I sand and then pull the lower layer of lining paper away. I then cut through the upper layer of paper.
By using two layers of paper, at not point will the foam or filler be in contact with the floor. The floor is free to expand/contract without issue. You will end up with a 0.52mm gap at the end of the job.
More importantly, you will have a clean 90 degree between the floor and skirting. With caulks/polymers, you will end up with creep on to the floor.