Your partner can try to extend his arms to hold more of his weight further away from your body. This will work for awhile. Many couples love this position because of the face to face interaction that it brings. As your belly grows, you can convert this to capture some of what you love about this position, if you both just roll on your side. That makes it like a spoon position, without the rear entry.
If eventually your belly simply because too large to make this position comfortable, the pillows do work well at least for a bit of time. That said, the missionary position may be one that is limited in latter stages of pregnancy unless your partner is really strong or you're really small.
If you're worried about trying other positions, don't think about them all at once. Try one position, once or twice. See if that works for you. It's okay to be a bit adventurous.
One of the great things about this position in the latter part of pregnancy is the fact that it's harder to get much depth of penetration. So if you're feeling sore or worried about bumping the baby, your belly will prevent that from happening for most women.