Co-sleeper cots have different height settings for the mattress, the idea being that you can change the height to match the height of your bed. However you could always get a cheap cot which has a removeable side and then cut the legs to fit. My friend did this but the cot was too low so she got some of those elephant feet things the elderly get given to make their sofas the right height and put them under the cot legs.
We have this one: www.mothercare.com/Mothercare-Bedside-Cot/815448,default,pd.html but we bought it on ebay for £35. We had the mattress on the lowest setting and then had to chop a bit off to get it low enough to fit by our Ikea bed. We had it up against the wall on one side (tiny bedroom!) so no need for any fixings. DS slept in it next to our bed until he was 10 months and then we put the side back on and he's still in it happily at 2.3. We'll get him a bed very soon.
We have ikea cot - most can be assembled minus one long side - very sturdy - fortunately we also have ikea bed so mattresses line up (foam piece and cot bumper wedged in far side gap - there's a guy an eBay that makes coach built pram mattresses that can send mattress foam cut to any size needed) my DD wriggles over if she wants me and she's close enough that I can hear her. Really good system. At night I can lie across both beds to feed and inch away when she's asleep - plus it's supposed to be big enough to last until 2 as its a cot bed (hence why you can assemble minus a side).