Too Cold????????

i am just wondering what happens if the plant is a little too cold. its winter and ive noticed it being rather chilly in my space. and when i touch the plants they feel very cold. i do not have a thermometer, but i plan on getting one soon. any thoughts?? whats the lowest temp they will live in. and what is optimum 60s??

i believe anything below 60 will kill them from 60-65 they are in almost a hybernation state very low and slow growth