You can get a bed alert pad similar to this one on Amazon, where if he shuffles off the pad or can get himself up from his bed, a little sound will go off to wake you up.
Just a suggestion to consider, but I think the button thing mentioned earlier might be better and more affordable for you.
Thanks for the ideas. There are definitely issues with the pressure sensors because of the weight of the matress itself and any potential tossing and turning. The ir break sensor would probably be an issue too if I decide to get up in the middle of the night for anything. I was thinking about using thishttps://www.amazon.com/Smart-Caregiver-Bed-Alarm-Sensor/dp/B00489SJ4S sensor for old people and connecting it to a regular alarm clock. My only problem is that the sensor is built to alarm when someone gets up. I want it to do the opposite, and only during certain times of the day. Any suggestions?