DD is nearly 5 months old and I only front carry her. I'm scared of trying a back carry - I gave it another g today and it just didn't work for us. You can carry on your front as long as you like. At some point it will start hurting you but that will depend on how used you are to carrying your baby like that (so you've built up the muscles), how much your child weighs, how supportive the wrap you use is, what carry you have tied and how well you have tied it.
I'm wearing DD just now. I have been doing housework and have stopped for a rest. If she was on my back I wouldn't be able to sit comfortably back.
As for recommending a wrap.. I have an awful lot of them
I would say the most important thing is to choose a pattern and colour that you like. The wraps I use most are:
2 Calin Bleus, one burgundy, one olive. These are gauze so they are much thinner than others and much cooler. I find them amazingly comfortable but I don't know if they will be next summer as they will have less support for a bigger child. They are my cheapest wraps but like I say, won't be as comfortable for as long.
I have a Didymos Bears that was blue and has been dyed eggplant. If it was still blue I wouldn't really wear it but I love the colour it is now! It is a very thick wrap and will be supportive well into toddler years (and beyond!). I find it a bit thick for some carries with DD being young at the moment but now I fold it in half lengthways it is really good.
I have a Didymos Pfau which I may dye Woodland Brown or I may keep it black and white. It is a really supportive wrap and will be brilliant when DD is older. The only reason I don't use it as much just now is because I prefer the colour of my other wraps
I have a Girasol Earthy Rainbow. I use this one most because I LOVE the colours!!!!! And of course the more you use a wrap the softer and snuglier it gets so the more you want to use it
At this very moment I have DD sound asleep in a Stochenwiege Natural Leo. I'm going to dye it lavender if we ever get on top of the washing! I would recommend you get a Leo as they are very supportive but with a bounce to them because of the diagonal weave that makes them very comfy! My Leo is the most forgiving of my wraps - I know I've not tied it that well but nothing is digging in. It ticks all the boxes for a wrap that will work with all weights. I wish I'd got the turkis (turquoise) one as it looks gorgeous! The natural one can be dyed whatever colour you'd like though and is more brown than I expected - it's quite nice actually! It also comes in marine or red. I guess you would need a size 6 (4.6 metres) and that would cost £52 which may seem like a lot of money but saves buying one and then needing another later on. I ordered mine from Big Mama Slings and there were no delivery charges.