Let's see if see if we can't clear some of this up.
From your description there are two most likely culprits. First, you baking powder is weak. Or, second, you're not handling the biscuit dough properly.
In the old days, people used baking soda for leavening. One of the inconvenient aspect of baking soda was that it required acid to make it release the carbon dioxide gas which leavens the dough. This is where the custom of using buttermilk came from, by the way.
Then single acting (SA) baking powder came along in the beginning of the 20th Century. That's the sort foodnfoto described and gave a recipe for. As she said, it's simply baking powder plus a dry acid. Once SA is mixed with any liquid, the dry acid (usually cream of tartar aka tartaric acid) goes into solution, starts reacting with the baking powder, and voila! Carbon dioxide gas is produced and "raises" the dough. The problem with SA is that all of the lifting action finishes not long after the liquid is added. This means you have to work fast putting your dough together, patting it out, cutting it and getting those biscuits in the oven. SA is still very popular in Canada, Europe and with people who want to avoid the aluminum pyro-acids in double acting powders.
Double acting (DA) baking powder is the most common kind in the the US and is the primary leavening agent in almost all self rising flours. DA not only has a dry acid, it's got a second "pyro acid" which is activated after dissolving in solution by heat. In other words some of the rise is saved for the oven. This means you don't have to work as fast which is important for a lot of bakers.
Both SA and DA degrade over time and with any contact with moisture. If you were using a recipe which had been successful for you before, my guess is that your flat biscuits were the victims of degraded baking powder. If you've never (or seldom) baked your own biscuits, the problem may lie with the baking powder, the ways in which you handle, cut and put your dough on the tray, or the recipe itself. Without knowing a lot more, it's hard to pin the problem down.
With all due respect to Ed and your Mom, the problem is not elevation. Elevation makes leavened good rise quicker and higher. The proper adjustment for baking powder leavened good is to reduce the amount of baking powder by 10% for each 3,000 feet above sea level. It's also generally recommended to cook at a slightly higher temperature than you would at seal level in order to kill the rise sooner. About 10 degrees per 3000 feet. Other recommendations for elevation have to do with the flour/moisture ratio; but rather than getting specific let me say that an exact ratio is not important with biscuits and the ideal ratio can only be determined by touch informed by experience. All the fussy adjustments are more for cakes than breads.
foodnfoto's recipe looks good to me. Note that they succeed only because she uses very fresh SA for the extra puff. If she used DA for the additional baking powder her biscuits would have a metallic taste. However, if you're at altitude, all that baking powder might be massive overkill on the baking powder if you're over 5000'.
If you like, I'll be happy to give you basic biscuit technique; along with a basic buttermilk/AP flour recipe; plus enough understanding of the process so you can improvise a little -- cheesy onion biscuits, herbed biscuits, and other things of those sorts. That said, if you already have a successful recipe, replace your baking powder and/or self-rising flour first, and try again before moving on to a complete retool.