I've been tandem feeding for 8+ months now! No regrets and wouldn't have done it differently, tho I think I'm about ready to try weaning soon, as my oldest is now 2 and often wants me instead of her dinner!
My daughter was only 7 months old when I got preg with my little boy. She (and I!) were no way ready for weaning and she couldn't tolerate any kind of dairy products (got red spots around mouth) so I was determined to persevere! I think I continued to have plenty of milk until I was around 6 months preg, tho I know it varies for different women. But Abigail continued to bf even when I was fairly empty, just as a comfort thing really. But I didn't want to stop her before she was ready. She finally took a bit of milk (mixed w/ liquid youghurt) at 12+ months, so that was good when my supply went down, so at least she was getting something in addition to food.
It can be a bit difficult if your breasts are extra sensitive when you're preg (feeling sore), but I just kept on - so it is possible if you're willing!
Abigail is quite petite, so I didn't find the position too much of a problem, though will probably vary depending on how big your bump is. I think towards the end I often preferred to lie down with her so I didn't have the weight on my tummy.
I didn't have any problem with colostrum or different kind of milk. She just shared the colostrum with her baby brother! And was overjoyed when I got a lovely huge milk supply! (I'd already had an oversupply for her when she was a baby, so I had more than enough for the 2 of them!) It was really cute when she'd point to me and say "there's lots of milk in there!"
Recently her top teeth seem to be sinking in to me (don't know why, as teeth aren't supposed to interfere if they're latched on correctly), but I'm getting quite a bit of pain at times lately. Not always by any means, so don't know what is happening. But I think I'm probably ready to try weaning her soon. Benjamin is only 8 months now and I'm planning lots more breastfeeding for him, but I think I'm ready to just do the one. But at the same time, I don't want to force it or rush it either, so who knows...might still be breastfeeding when she's 3! lol
But I'm happy with tandem feeding. When I was younger I don't think I ever knew anything about the idea. My mum weaned each of hers at 22 months and all 7 of her children were naturally spaced at about 2.5 years. But I was exclusively breastfeeding my little girl and my periods came back when she was only 4 months, and I was preg by the time she was only 7 months! So....not like my mum! Right now though, my youngest is now 8+ months, and with tandem feeding the both of them, still no periods & no pregnancy! Guess it's different each time.
Well, sorry to post such a long post! But maybe it will be a bit helpful to hear from someone who is doing it now.