Boy oh boy,
There is a FICO scoring perspective and a mortgage underwriter perspective on this.
If those are your only accounts here are the factors at play -
1) Very short history....under a year - this will not become a positive factor in a year
2) More regular CC accounts will not help....you are probably near maxing out on those tradelines
3) Your utility is very low overall but could be lowered down to under 5% on one account....maybe gaining you a few points (0-5).
This is all guess work but I see your 2 options as let your history grow for a bit over a year doing nothing but maintaining your current fiscal/FICO responsibility or 2 immediately go for 2 new accounts that will give you points in the mix category (but may hurt your score in the under a year timeframe).
Here are things you COULD consider:
1) A 1,000 loan that you would stretch out until you are ready to get a mortgage.....ie have like 200 bucks outstanding when you apply for a mortgage....this will allow you to get points for an installment loan but would likely not concern a loan officer.....if you take this option it will slightly lower your already very low average age and I would do this now...and not apply for a mortgage for 1 year.
2) Apply for a store card that you will use. Best Buy, Macy's, JCPenny's, Gap/Banna Repub/Old Navy, Victoria's Secret.
Those two types of accounts can add maybe 15-20 points to your score but they will ding your age and your new credit category. The new credit ding will go away in 1 year, so if you go this route I suggest not applying for a mortgage until just over a year past the date you open these accounts.
Your other option is to wait until about August 2009 doing nothing but ensuring no late payments and have only one balance report 1-5% util at the time you apply for a mortgage. We have seen people with 2 years history wind up with 720....that will get you near enough to the best mortgage rates if your income and DTI are in line. I defer to the mortgage people on that front.