heating please look

hello there i need to put my plants in for sexing/flowering there are 10 plants they are all around 3feet tall (big) but where i am growing the temp stays at around 19/22 dergree's with my light on
without it on its dropping dangeriosly low.tested it the other day
so i need a heater ok 1 that i can set so it tunrs on wen the heat drops below 18,dc and turns off when it hit say 24/dc could any1 find me a link wher i can buy 1? would prefere some where in uk need it asap! thanks :)

there are loads out there i have a good delongi one sorry for the spelling argos sell them

SMooth, with that much of a temp fluxuation and big plants, you are really courting mold growth... condensation

but it sounds like you are aware of this potential problem...
Make sure you have good air circulation...

the plants should always be moving a little bit..
especiually when they are packed in tight!!

: )

my question still not been answerd :(