Thin folks can't believe that larger people still have missionary sex. There are two secrets that a bigger man must know if they are going to have missionary sex. The first is how to support his own weight. Using your arms or keeping your torso vertical above your hips are two solutions to this problem. That way, you won't crush anyone.
Another secret that a man can use is communication. Some partners may want to feel your weight upon them. By asking "is that too much for you" you will know how much of your weight you can put on your partner. Someone one told me that "A gentleman always supports 1/2 his weight" but I don't know if every woman wants that. Some women like the sensation of their partner on top of them.
If you are a man making love to a larger woman the objective should be fairly straightforward. You need to achieve penetration. If her stomach is in the way, one method to keep it out of the way is to stack a number of pillows under her buttocks. This will put her entire torso on a downward slope. Causing her stomach to roll toward her chest. This position will also help you stimulate her g-spot.
Before you go trying any funny business, you may want to stretch out a little. There aren't many things more embarrassing than going into work with a sex-related injury. On some days you may be able to come up with a good excuse but if you come into our office on the day after your anniversary with a sore back, you can expect someone to say something very funny.