The reason they say not to put pillows in the crib is because it may increase risk of SIDS. After age 2 the risk of SIDS is extremely unlikely. So most of the no pillows, no overstuffed blankets, and no stuffed animals suggestions are kept until age 2.
Inclining the mattress should work well for congestion and comfort. Laying the baby on their front is also a big concern for increasing SIDS risk, but with that the general rule is to keep them sleeping on their back until they are able to roll over on their own with ease. They are also supposed to be given supervised tummy time everyday to help increase arm and upper body strength, and to keep from getting a flat head in back.
Please don't take this too lightly. My sister's last baby died at 2 months from SIDS. All her children were put to sleep on their belly. My mom even encouraged this, because she was told to do it when we were babies and we were all fine. It isn't that they will die from SIDS or probably die, it is just that the risk is increased, but why take any chances?. The chance of any baby dieing from SIDS even with many increased risks is low, but these things do increase the risk. There is a lot of questionable information about SIDS, but it is a risk that is worth trying to prevent. With my sisters situation he was fine that morning when she woke up. She checked on him (he was sleeping, but fine) she went downstairs to feed and change her other two kids. She came back up 1/2 hour after checking on him, and he was gone. I don't want to scare everyone, but I want to make it clear that it is worth avoiding increased risks even if you think it's nothing to worry about. Don't fall into the trap of thinking "my whole family did this and we were all fine, so my kids will be too."