I have researched the issue on the web and found a solution : EltaMD non-tinted high zinc oxide moisturiser applied to the neck, decolletage and hands 15 minutes before getting dressed.

Tinted goes on the face and ears only.

I then talked to the nurse practitioner who advises me on all things beauty and she endorsed this solution, saying that the only better option is Alastin sunscreen with 19.95% clear zinc oxide that glides very well and gets absorbed instantly. Alastin is pricey, though, so I will stock with EltaMD.

I now feel supremely stupid for not finding this solution which really is obvious earlier, before I ruined so many collars.