Westies are terriers and as all terriers, very intelligent and in need of constant stimulation. A Westie is not a breed that faces that well being left alone in the house for many hours.
If you must actually leave him alone in the house ( specially considering that he is young and can still be easily taught) I recommend that you use a crate for the sake of your furniture. Crates sound a bit cruel but they are understood to be like a private little corner that the Westie will mark as his and feel safe in. Be careful never to use the crate as a punishment place after you introduce it but always as “his little corner”.
Also a constant flow of new and stimulating toys is needed. I know it is expensive but furniture is more expensive! Westies like stuffed toys and balls, preferably with a squeak.
In the end the better advice I can give you is, let him be with you the most of the time. You’ll both be happier.