The  key to keeping this houseplant happy is to water infrequently during the rest period right after it blooms usually the months of February and March then it can go outdoors in summer in the shade only as you have done but a limp plant is usually due to do too much water during the resting time. Keep the plant on the dry side and cool in mid September and October when the buds are forming then water weekly while in flower. Repot right after it finishes flowering using a cactus plant potting soil. This plant likes to be pot bound so just go up one pot size more and do not let the plant sit in any drainage water. I think a clay pot is a better choice for this type of cactus as it breathes and does not trap moisture like a plastic pot does. Resist the urge to water so much and the plant will stop being limp. Every situation is different but during the resting period after it blooms many plants do well with water just once a month. Watering once a week seems a bit much. Christmas cactus also need cool conditions around 55 degrees right after it finishes flowering to force it into a resting or dormant stage. So cold and dry to put it to sleep after blooming then outdoors in summer with more water and water once a week when in bloom. Keep growing, Marianne Binetti