I need to purchase a new mattress for my parents and need suggestions. Recently my mother has slipped onto the floor a few times getting out of bed at night to use the restroom. We think the mattress is too soft on the edges and sinks when she is trying to get out of bed and then slides onto the floor because of the mattress sagging. The current Mattress is new (foam), but I believe she needs a firmer mattress to have stability. (She does have a walker and bed rails currently as well) Any recommendations or advice is greatly appreciated!!! Right now she is sleeping on the lift recliner with is likely making her back pain worse.