treacle I'm savouring being able to sleep on my back/front as long as possible this time. Don't think it matters at this point as it's not heavy enough to do much, and I was SO FED UP of sleeping on my left side by the end last time.
toffee the advice is no longer than 2 hrs in a car seat as their necks aren't strong enough to hold their airway open in that position apparently. I think so long as you alternate it's fine.
I agree with delation on carriers. Hip issues aside (there's a lot of debate on this that I won't get into), carriers like the bjorn will kill your back after about 6 months. Carried DS in a stretchy wrap until about 8 months when he fit in the ergo which is great, my husband prefers that for days out to the pushchair and carries him easily at 19 minths. I also have a woven wrap and a ring sling, both great.
sundays I've resigned to getting a double too, DS will be 25 months and it's not flat terrain where we live - can't imagine having sling + single buggy as only means of getting out. Looking at mountain buggy duets on eBay as we have the single and love it - tried my sister's Phil and teds when we visited, with her toddler in front, but DS hated being in the back and lifting him in and out of the back was a massive faff.