We stayed at Four Seasons in Elviria a couple of years ago. Its quite an upmarket area with lots of quality apartments. Not much in the way of shops, there is a small commercial centre with a supermarket, several restaurants. The beach here is lovely. I think the Santa Monica apartments are on the opposite side of the dual carriageway to the beach so you will have a good 10 minute walk at least.

Personally I think a car is essential here. We visited most of the major towns along the Costa del Sol. In August the main coast road is extremely busy (and slow). There is a toll motorway nearby which cuts down travelling time considerably if you are prepared to pay.