I switched from breastfeeding to exclusively pumping when the triplets were a month old. I know most moms do the opposite, but there were a lot of factors that went into my decision. You can read more about that here.
No pediatrician will recommend bottle propping. In fact, many articles state the hazards of bottle propping. They claimed that your child could choke, overeat, suffocate from bottle props, develop poor eating habits, and even suffer psychologically from a lack of intimacy. Some of those things could happen if the babies weren't supervised, but those warnings always seemed to be fear tactics from attachment parenting articles.
With all that said, I was the one and only person responsible for feeding three infants and a two year old for ten hours a day. Bottle propping saved my sanity. My babies weren't crying because they were hungry and I couldn't feed them all at once. We stuck to a schedule and everyone ate at the same time. Nobody choked, suffocated, or had trouble bonding with me.
I began bottle propping when the triplets were six weeks old. (Keep in mind, my babies weren't preemie, nor did they have any problems sucking or swallowing.) I tried boppy pillows and receiving blankets, but I could never get the angle quite right. Of all things, I found my son's stuffed animals worked the best. They were firm enough that they kept the bottle in place.
Initially, I bottle propped one baby while feeding the other two by hand.
The problem was, when someone needed to burp I had to disrupt the feeding. I realized it was faster and easier for me to bottle prop all three and sit beside them while they ate. That way, if anyone started to cough or wiggle, I could immediately adjust him/her without stopping the other two from eating. The first baby that finshed (normally James) could easily be picked up and burped without bothering the other two. And feeding time was still bonding because I would sing or read stories while they ate.
If we were running several errands and the babies were getting hungry, I fed them in the parking lot using thick blankets as bottle props. (Again, this was always supervised. I never gave them a bottle while I was driving at this age.)
I used pillows as bottle props and placed something weighted underneath the bottle to prevent it from slipping.
Now that the triplets are 8 months old, they are each able to hold their own bottles. Gone are the days of creative bottle propping. Hello, independence!