Use the stock saddle and get some saddle time. Comfort on any saddle is usually determined on how well your ass can adapt to the saddle and the consequent time on the bike. If the discomfort continues after 2-3 weeks of constant riding, then consider a different saddle. Padded saddles are generally considered to be less comfortable and as you have already discovered a wider saddle is not for you.
Put the saddle that came with bike back on and ride that for a while. Soreness from an activity you have not done in a while or do not do on a regular basis will cause some sort of discomfort at the beginning. Give it time.