It´s same as in English, we´d say: Cuídate or cuídate mucho.

Hola, As you would like to express a wish, you need to do it with "subjuntive" : "Espero que te mejores pronto" ( hope you get better soon), "espero que puedas descansar o suficiente" or "imperative": "cuídese/cuídate y/o descansa" ( take care and get a good rest) Espero haberte ayudado, un saludo