In order to do this, you must collaborate iTunes Apple IDs, but split off iCloud accounts. For you, it sounds like sticking with iCloud contact syncing will be good so that you (and your wife) will have your contacts synced across multiple devices.
First you must decide who will stay on the "primary" account - this is the account that you already have. The other user (probably you), will setup a new account for iCloud.
Go to https://appleid.apple.com/ and get a new Apple ID. Next, on your iPhone, go to Settings.app -> iCloud. Scroll to the bottom and select "Delete Account". Don't worry, it's basically just signing out of the account on your device. When prompted with the contacts, select "Keep on my iPhone" (very important).
After "signing out", sign in with your new Apple ID. You may need to change accounts on your Macbook as well so that contacts are synced over. After you are signed into the new iCloud account, go to Settings.app -> iTunes & App Stores, and make sure you are signed into the old (your wife's, or the "primary" account) account. This way, you can make purchases with the same credit card, and you can perform updates on apps.
If you wish to share calendars, you will probably be best off using Gmail for that. Unfortunately, sharing reminders and notes won't be possible with the new setup.