There have been other suggestions in the thread how to avoid ending up in this situation that I think are good, like put your work bag or purse in the back seat too, or if you’re really concerned, take off your non-driving shoe and put it back there.
Kidsandcars.org does great work too, and clearly the message is getting thru to auto manufacturers too.
My boss has a new ford ranger, it reminds him to check the back seat if it detects weight. There are lots of ways to prevent this happening to you, figure out what makes the most sense for you and go with it.
Also, you’re going to be a great parent. I don’t know how I know this, I just do.