I'd use the powertin for popping out too tbh. with a sling and cheapo stroller.. you'll be weighed down with baby, bags, all your stuff and having to push something thats nowhere near as nice/easy to push as the jane pushchair!
A basic fabric ring sling would suit well especially for a new born. Google big mama slings and have a look there - the ladywho runs it is also really really helpful if you want advice. I would avoid anything too think and rucksacky as it's too difficult to feel what your lo is doing - and its very important that they have a good position when they are tiny... I'm also addicted to my babyhawks which are sooo convenient.I would also recommend the yahoo sling group UKbabywearingSWAP as you can get really good deals on 2nd hand slings.
I love wrap slings, I have a few I use in jersey and fleece that I made myself. They're really easy on the back (I have a bad back and am not supposed to use a pushchair) and I still take my 2 year old out in one when I need to.
Where do you live? You should be able to find a sling use group near you where you would be able to pop along to a meeting and try out a bunch of slings - or at least look at some different styles and designs before you buy them. You could try looking for your local group in the forums bit of the babywearer website.
Either a wrap sling (which do have a bit of a learning curve, but are lovely for littlies), or a MeiTai. I carry my 2 year old, who isn't small by an means in a Toddlerhawk - a bigger BabyHawk - and it doesn't make my back hurt at all.
Its def much more practical than a twin pushchair imo.
If theres a Slingmeet near you, then you can try different slings, or just buy second hand - if you don't like them you just sell on for much the same price
I bought a ring sling before I had ds and struggled with it as it just hurt my back so much. He was a big baby and now at 5 months weighs 23lbs so is not exactly an average comparison but I couldn't do it (and I'm not a lightweight!). It didn't hurt around the sling itself, was lower back pain and I had to give up in the end and only use the pushchair
I bought a freedom sling at the Baby Show when I was about 8 weeks pregnant with dd. That dd is now 22 months and I've got an 8 week old dd2 and I've used sling about 4 times. I way prefer the baby bjorn.
You say your 2 year old's not a great walker. I'd go for a double if I were you or at very least a buggy board. I got a bargain double nipper on ebay and while i have the opposite problem and dd would really prefer to walk (or run), it's a fab pushchair and already (8 weeks on!) I've got my money's worth.
I have a Kari-Me and I have also checked out (and given as a gift) the Moby. Both are great slings, fab for little newborns and actually really easy to use.
I will freely admit to being sceptical and daunted when I first got it (so was 2 month old DS) but within a day or two we'd got the hang of it and he lived in it thereafter. Made the pushchair a bit redundant really!
Well I don't have two (yet) [hopeful TTC emoticon] but I can say I've used a buggy twice with DS since I gave up on the pram when he was about 4 months old. But yes, you can keep sling from newborn through to walking if you want to.
You do need to be careful about the buggy pushing though, as pushing a buggy is really not brilliant at all for your back so the extra weight of slinging could make your back hurt if you are adopting bad posture to push the buggy. (I wonder if this was the problem for Haylstones??)
Wraps are brilliant and not really very hard to learn. I used a Kari Me when DS was little - used to tie it on in the morning and pop DS in and out at will. It took me oooo 20 seconds to put DS in or out. Say a minute (maybe less) to put wrap on at the beginning of the day. Anyone who knows me will tell you I'm a complete clumsy idiot and I learnt how to sling in less than a day. The only problem with Kari Me is that it is quite hot, and when baby is heavier (usually around 6 month mark) you'll want to move on to a woven fabric for your wrap. It's great though.
I am a crazy mad babywearer - it's been so good for DS and me - so I would say yes, go for it but make sure if you're using a single pushchair as well that it's fully adjusted to be pushed ergonomically and with a straight back. Make sure you look straight ahead as much as possible while you walk with the sling and wear good supportive shoes (very important for back care). Work up to it gradually. The best way to train your back muscles is to get some brisk fluid walking going (not shuffling around the house), so as soon as you're happy your tie is secure, get out and walk where you can put your eyes on the horizon. Do short walks like that before attempting to go round shops and the like, which is deathly tiring and bad for the back whether you buggy, sling or go childfree.
I should add that although I've made it sound like a palava, I'm firmly of the opinion that slinging baby did more for my core stability than the physio run postnatal exercise class DS used to scream through. So I would recommend it for your benefit too.
A ring sling is great with a newborn as you don't have lots of weight pulling on one shoulder, but once they hit about 3 or 4 months you can only wear them comfortably for half an hourish. By that age a Mei Tai works better as it is both shoulders so spreads the load.
If you got a non stretchy wrap (normally called a woven) you can use it in so many different ways (baby lying down, upright facing you, cradled etc) and then for hip and back carries when older so a decent wrap would be my recommendation if you want one to do you for all ages.