Also consider a seiza bench. It will still stretch your knees and ankles a bit, but I've found it's easier to assume a stable posture than fidgeting on a cushion or sitting in a chair.
Regarding short bursts, I recently read this advice by Thrangu Rinpoche:
When one meditates, do it for a short time; but do it again and
again and again. The whole point is to develop a habit of
meditation. If one meditates at first for too long, the mind just
becomes more and more agitated and difficult to control. If one
meditates for a short time and renews the session many times,
then each time the mind will be fresh and clear and able to settle
down more easily. So meditate again and again until the habit of
meditation grows stronger.
You start short and frequent and lengthen the sessions when you're ready or able. You'll know you're ready when the time is up and you think, "Holy cow, am I done already?" And some days will be better than others. Not so long that you become like a covered pot boiling over, but not so short that you never get to work with the juicy feelings of resistance, impatience, frustration... A lot of fun for sure
My current strategy is one or two good, long sessions with lots of shorter ones interspersed when I find a moment. 5 minutes here, 10 minutes there... Monkey mind is constantly reinforced through our daily habits and lifestyle
so it's important to keep the thread of mindfulness going through frequent meditation. The plus side too is the more you familiarize yourself with watching, resting, the more your mind gains confidence in its ability to let things go.
Whether or not you'll be able to benefit from the lessons of physical pain is a personal matter. I think some days we're like 1st graders and the situation is a calculus class. We just won't get the lesson no matter how hard we try, so we have to be gentle with ourselves and stick with 1+1.
Please take the above post with a grain of salt.