Did you try:
1. Rubbing something that smells like him on the bed to show him that it's his and not some scary new weird object. (rubbing him with a towel, then using the towel to rub the bed, something like that)
2. Doing a training session with it- throw treats on it to get him to go on it, then ask for a lie down- this gets him used to it.
3. Feeding his meals on it.
At the same time, depending on the temperature where you are, maybe he really is fine without it- but if he does seem to need it to be happy/healthy, maybe some of these will help?
1. Rubbing something that smells like him on the bed to show him that it's his and not some scary new weird object. (rubbing him with a towel, then using the towel to rub the bed, something like that)
2. Doing a training session with it- throw treats on it to get him to go on it, then ask for a lie down- this gets him used to it.
3. Feeding his meals on it.
At the same time, depending on the temperature where you are, maybe he really is fine without it- but if he does seem to need it to be happy/healthy, maybe some of these will help?