As far as I know, version 7.3.25.K is the last one, that allows application updates in Sailfish. It works for me. Play services you can update from Jolla Android Store.
Very easy to obtain older versions of Play Store via Aptoide, although remember you still have to accept "Update" to install 7.3.25.K if you are on 4.5.10
touch /opt/alien/data/app/com.android.vending-1.apk chattr +i /opt/alien/data/app/com.android.vending-1.apk