I'm 5'9 and a bit shy of 200, and suffer from sciatica a few times a year. I, too, am hesitant to buy the mats -- partially because of expense, partially because I'd like something a little more attractive in my kitchen, which is not a showplace to begin with (very 40s country looking, built in the 80s .... I mean the 1880s).
The things that help, to me, are some already mentioned, that is the small foot stool for the leg that is bothering me, and not a barstool, but an old timey kitchen stool that is also a stepstool you can sit on (oh, brother, not explaining it well). They are made, I think, by costco and easily available by mail order.
I have an eat in kitchen, and the obvious answer at times is to do the more tedious jobs (chopping, mixing) that you don't need to stand up for, sitting at the kitchen table. A lot of the prep work simply does not need to be done standing at the kitchen counter. Maybe because she had similar back problems, maybe because doing the prep work might be a multi-person affair (when relatives were visiting especially), but when I was a kid, a lot of the prep work for big meals might be done outside on the picnic table or at the dining room table, shared. Now, silly as it sounds, I have to remind myself of that and take beans I need to trim or other such jobs and just move them to the table or to a chair somewhere else.
