LOL the reason you can't find an answer to how much you should nurse your baby is, all you need to do is feed him whenever he's hungry, and end the nursing session whenever he's satisfied. My 10-month old daughter even stops to look around and play before she's done, so I offer her my breast another time or two, and she might go back to nursing another 5 minutes.
It's the reverse of what you think: you're reassured by feeding an 8-oz bottle if that's what the "experts" say he should get, but actually, how do they know? What if it's hot and he's thirstier than usual? What if he is more or less active than the average baby, so needs more or less than other babies? When you nurse your baby, your baby eats as much as he needs to.
(By the way, in fact, what is taught is, a baby should get as many ounces in breast milk or formula as he is old in months. Five-month olds should get 5 ounces per feeding. So, if you're talking about your 5-month old, he should definitely not be getting 8 ounces. Taper down.)
The solids problem is the same as the formula. The way you're feeding him, and the amounts, anyway. They're interfering with your supply. Easily fixed. The La Leche League leader I asked about feeding solids vis a vis my supply told me something that made so much sense to me, once she said it. Feed solids *after* you nurse your baby. Then, he's only getting a little. And that's all he needs till he's a year old. As they say, "before one, it's just for fun." The solids foods are not supposed to replace your nursing in any way, but just be in addition to.
(Sometimes I cheat and give my daughter a couple of bites of my banana or apple, or soy yogurt or whatever about an hour after nursing, too. Doesn't seem to hurt anything, my supply is fine, and she is nursing as much as she did before.)
As for gulping and swallowing noises, my guess is, as long as he's staying latched on, he's getting enough to keep him interested. I think that you're not hearing the eager feeding noises because he is getting filled up on solids.
Now, this part is VERY IMPORTANT: feeding large amounts of solids, especially to the point where it's replacing much of the daily breast milk intake, can be a serious hazard for a baby because the main - practically only - source of food till age 1 is breast milk or formula. You need to reduce his solids to avoid this. But I wouldn't risk it.
Absolutely don't worry that he won't get enough breast milk. Your body will supply all that he needs. This is how we women are built! Or else we wouldn't have made it this far through human history. If you're "not making enough" in the immediate term, he'll just nurse more frequently for a day or two. This tells your body to make more milk. If this becomes a nuisance, just take him to bed, snuggle up and catch up on your sleep :) Or read a good book. (If you're not familiar with the side-lying nursing position, in particular, experiment a little till you get comfortable. Try a pillow to support your back. Try the top breast or the bottom. But do try it. It's so worth it.)
L.
PS instead of jarred baby food, try just mashing up and diluting with cooled, boiled water, foods like bananas, avocados, sweet potatoes, and squash (the best foods at this age). It saves you a lot of money and is way healthier for your little one. You can get BPA-free plastic food cube trays - like ice cube trays, only safer for babies - from cottonbabies.com. This way you can just pull a cube out of the freezer, add a little boiling water to it to help it thaw, stir it up and you've got your "meal"! CHeck out Ruth Yaron's Super Baby Food for more info. Great book.