Getting ground cover on very sandy soils can be problematic. Does the lawn have shade too? That will make it even harder. The best grasses to try in your situation will be fine fescues including Chewings fescue, hard fescue, and red fescue. Here is a link to a grass seed mixture that has all three: http://earthcarpet.com/care-free/ This is a Wisconsin company, so you should be able to find this for purchase in your area. The website has phone numbers and email addresses of several sales offices. Good luck and let me know if you have any additional questions. I am not an expert in non-grass ground covers, but those may be something to look into.