Calculating your personal inflation rate

Well you definitely need a large sample. I can't think of anything that keeps pace with inflation in lockstep fashion. Most prices just get adjusted every now and then. This is either the cause or the effect of inflation, very much a chicken or egg problem. When you consider thousands of products and services, the cause/effect of inflation is much more observable on a short-term basis. Go to the other extreme, say just one product, like a Timmie's large coffee. They raise the prices on those like what, every couple years?

It also becomes a challenge when you consider technology. The typical phone today costs much more than the typical phone 20 years ago, but the typical phone today is really more like a phone, computer, music device, digital picture camera, video camera, GPS, and more all combined into one convenient, small package. If it were possible to combine all those into a small package 20 years ago, what do you think it would cost? And, remember, these are all pretty powerful components.

So then in an attempt to avoid this, you just follow one specific product. The Sanyo 2000 cordless phone cost $X in 1997, $Y in 1998, and $Z in 1999, but then it got retired and replaced with something better. Would it be fair to compare that better product's price with the price of the Sanyo 2000?

If you try to follow the price of some similar product over time, e.g. a typical bare-bones wall-mounted phone nowadays vs in the past, then you actually do have a fair comparison. The price of such a product has probably risen less than the general inflation rate. BUT it's not a valid comparison. It's not representative of the actual spending habits of the general population, which is really what you want to know. Most people do not buy those bare-bones phones; they buy smartphones.

OR you can look at the prices of items that are much less complicated, e.g. the price of a 4L jug/package of milk. But if that's all you look at, then, again, your comparison will be fair but not valid. People don't spend money on only those items.

As times goes on, people are spending proportionally more money on "complicated" items, and that significantly complicates the determination of a valid general inflation rate. That should be my TL;DR.