Which type of cabin will you book? The smaller R-ships have tiny bathrooms unless you book a penthouse or above. We don't care but many people find them unacceptable. There are tons of Youtube videos that show the different ships and suites (limit it to the past year or so to get current videos). The R-ships are Regatta, Insignia, Nautica, and Sirena. The larger O-ships are Marina and Riviera (plus there are new A-ships that haven't sailed yet).
You can book cruise-only and skip air and/or O-life (the pick one perk choice). It can be added later (before final payment I think) if you want it. If you get O-Life, don't choose the OBC. You pay $300 to get $300 non-refundable OBC. If you want pre-paid OBC, buy yourself "gift" OBC which is refundable.