Hi! Wanted to chime in with some thoughts...
First of all, it may just be me, but is your DH's concern about your body changing a healthy concern? It's hard to tell in posts/print, but I just wanted to ask because it's not usually the first thing a loving husband who wants to have a family would mention. Making sure wife and child are healthy, happy and loved should be the primary issues, not how much the woman's body may change... Again, if I'm misreading anything, I apologize. It just gets me steamed thinking about someone's husband being that kind of jerk...
I've had 4 babies 'later in life' <haha> and worked out through all of the pregnancies, though I think the first one was the most cautious. We had trouble getting pregnant, and it was my first, so I probably didn't do as much as I could have. NOT THAT I'M COMPLAINING, mind you!! A healthy baby is so much more important than the pounds gained!
One caution I wanted to give is not to focus on the pounds, but to focus on eating healthy foods in reasonable quantities (you don't literally have to 'eat for two'...more like one and a quarter
) staying active and limiting stress. Honestly, you have to think about what your goals are for the nine months - making a healthy baby is probably number one. In my experience, you can't say 'I'm only going to gain X pounds' and make that a focus. Every woman's body is DIFFERENT and every baby is different. Your body will gain what it needs to, and it will lose the excess afterwards if necessary, as long as you keep your same lifestyle and eating habits.
Really, it's totally normal to gain 40 pounds (or more, if you're underweight to begin with). And it's also totally normal to gain less than 20. There's no absolute 'right amount' and you won't know what's normal for you until you've been down that road. Having a baby is a LIFELONG committment, so your horizon has to shift a little. The nutrition you provide to that baby for those nine months will have some impact on that baby's entire LIFE!! How amazing and scary is that?! Skimping on nutrition or food just to maintain some silly notion of 'only gaining 15 pounds' is crazy, IMHO, when you think about it in the big picture.
My main advice has already been stated - listen to your body every day, not your scale or your 'scheduled workout plan'. There are some days where you will be so tired that it's all you can do to stay awake. working out on a day like that could easily lead to an injury or strain that you could regret for YEARS! (Once you mess up your back or knees, you may have problems for a loooonnnng time - not a good lesson to learn after the fact!). Be cautious, and be gentle on yourself. Your body will be doing amazing things as it grows another person, and there's nothing you have in your life that is more important than that.