At the temperatures you listed, there's no real need to warm the bed/blankets up before placing the baby down. Those are normal temperatures, and your baby won't be harmed by not warming up the blankets ahead of time.
The helpful guideline given to us by our last hospital & midwifery was:
Dress your infant in one more layer than you are comfortable in.
Since it's not feasible (or always safe) to add whole layers to a sleeping baby, you can replace thinner layers with thicker layers.
So, if you're only using a thin blanket and sparse pajamas, then your baby will probably be better off in full pajamas and a swaddled blanket.
At the temperatures you listed, we dressed my son in footed pajamas, a hat, and swaddled him in a swaddling blanket. Once he was old enough to keep taking the hat off, we removed that. Once he aged out of being swaddled, we'd just leave him in pajamas and cover him loosely in the blanket.
Your only major concern with removing the hot water bottle is that your baby might be used to laying their head down on the soft, warm surface at night. Their head is probably the only part of their body where bare skin comes into contact with the cool sheets. So, to fix this, vigorously rub the general area of the bassinet where your baby's head will be. The friction from the rubbing will warm up the area enough to be comfortable for your baby. I often did this for my son when he was a newborn.