I agree: a welcome change that AnnaLena posted her real name, made an effort to describe her circumstances and had clearly made an effort to search before posting πππ
Codeshares my friend - look for a Star Alliance or One World airline and most likely they will codeshare with partner airlines - if you can find that you will indeed have one ticket and one checkin for luggage
a month between SR and PP would be great - plenty to see and do to keep you occupied. Maybe not a month every year, but might depend on the friendships you make while you are there. In PP I suggest the Embassy Place Apartments - used to be Accor, maybe still is - lots of long stay residents who work in the embassies and are lovely people