The pole on our farm wagon isn't suspended either and when I took some lessons from an instructor/trainer/competitor in CDE - she was horrified.
We spent a good hour with her giving me ideas on how to "fix" all the "problems" with my wagon - including shortening the tongue (I just bought a mini tongue and will see how it works - at least with the smaller ponies); and how we might be able to get a welder to weld on some type of contraption that would support the tongue...
In the end, for the purpose it is actually used for, the wagon works wonders!!
*****
Your boys are really cute! UMMM... mine are 10 - 13" taller than yours! At least the ones I'm currently driving are. I do have some smaller ones coming up, but it will be quite some time before they are ready to drive as a pair (or more) and then they are still larger than yours are...
I understand about collar fit! Unless you want to do custom fitted collars (can be pricey), it is hard to get a good fit. This is part of the reason that "the big guys" use collar pads - it affects the fit. Different collar companies can use different patterns for the same type of collar - though most seem to be standardized (but understand I haven't been doing this long!)... Mostly I've seen the 310 buggy collar for minis & shetlands. Though I just bought a different kind and we'll see if I like it when I put my hames/harness on it. Every time I go to my "chosen" harness shop, I learn something new! The new one this past weekend - the collars state a size, such as 11, which is the number of inches measured on the inside from the top to the bottom of the collar. It may be called a size 11 - but it can be 11 1/4, 11 1/2, 11 3/4. As long as it's not 10 3/4" or 12" - the collar is called a size 11. That 3/4" can make a HUGE difference in how the collar fits the horses shoulders and how/where it holds the hames. The harness shop I use, resells or markets collars from the Coblentz Collar Company - who just happens to be right down the road... Some other companies that market Coblentz collars, really mark them up...
I believe that some of the other Mini drivers that do Draft driving use collars/harness from other builders/makers in the mid-west. I don't know who and don't know if they are willing to say. I remember being really tired and a bit bleary plus turned out it was just hours before I came down very sick at Nationals 2012 - but it seemed like I was being told ".... I can get you what you need..." rather than being given the source/manufacturer... Others I have spoken with either didn't know who made their collars or couldn't remember.
Also understand, with draft horses - the owners, trainers I've spoken with state - that a horse will often be heavier (winter fat, pasture shape, out of condition) at the beginning of the season (spring). As they work, they loose the fat, muscle up and become fit. This changes the collar size, too. They often have more than one type of collar along with a couple of different sizes and then also used padding to help with fit as they changed shape.
I tell you what - we never had so many issues fitting our riding horses with saddles and saddle pads!!