This seems like a blissful no-brainer to me, especially as you don't have to take your dh into account. I, and several of my friends, co-sleep with kids with the same age gap as yours, only we're a couple of years further down the line. We all co-slept with our dc1s and just carried on when dc2 came along. It's been great and sleep has been abundant!
We have a similar set-up to you; a cosleeping cot (DD2, now 2) attached to my kingsize bed (which I share with DD1, 5). DP, who requires very particular sleeping conditions sleeps in another room, although he is supportive of co-sleeping. I found that bedtime was particularly nice in the early days (bar a bout of colic, which needed a different plan) with getting both ready for bed together, then snuggling down to feed DD2 and cuddle DD1 to sleep. DD1 wasn't troubled by the newborn cries of DD2, neither was DD2 woken by the nightly howls of DD1's when she suffered a spell of night terrors. I was able to bf dd2 lying down, so the whole arrangement has been really smooth. DD2 still did the usual baby waking up when small, but demand feeding ensured she always went straight back to sleep, and I am so relieved that I never had to get up for anything in the night, bar the occasional wee for DD1 (potty under the bed, easy peasy).
Now they are older, it's the sweetest thing ever; they wake up together in the morning, as if psychically connected 
, reach across to each other and say little sweet nothings to one another: "Good morning...I love you...You're the loveliest sister ever." No kidding. My friends who are still co-sleeping / bfing children with a similar age-gap would also recommend the arrangement in a heartbeat.
Good luck, and enjoy the sleep!