I’m going to go against the grain (groan) and say that PVC is fine for you to learn position, and even for a year or two of energy work. In fact, the short power you need to put into your strikes with simultaneous other arm movement will probably benefit at least at first from having a bit of spring coming back at you. Hardwood doesn’t have this.
I think part of the obsession with hardwood is because they undeniably look cool, feel cool and fit with tradition, but PVC should do the job for a good while at least at a fraction of the price and if you have a bit of practical skill you can make a portable one.
BTW, I love wood, and I much prefer wooden dummies: I just don’t think they’re 100% necessary in your case.
Also, as Liddel said, it depends on what ‘energy’ you’re trying to work, but if we are assuming you’re not getting too esoteric and you’re basically talking about what I said, i don7t think you need to lose too much sleep.
As for concerns about the type of wood, what people around the world know as teak refers to approximately 170 kinds of tree, so anyone insisting on that is simply playing into the hands of unscrupulous timber-traders! The best hardwood to go for is simply a good, close-grained local hardwood, preferably dried over time (but that is exorbitant) but kiln-dried has advantages too, and thus less susceptible to warp and cracking.
I know people who have imported fine sculptures and woodwork from other countries only to find they have not liked the atmospheric conditions locally and have started to warp and crack, and in soe cases this goes for antiques which have been fine for centuries until moved to another part of the world too.
BTW, some people will argue that oaks for example, which have preservatives known as tannin (tannic acid based - used for tanning leather, and incidentally the stuff that makes your teeth go brown if you drink a lot of tea/red wine) are good for toughening your hands over repeated hitting (it’s also a minor antiseptic/astringent). I’ve never seen any evidence of that, but it may make sense, especially if your wood is relatively fresh.