This would not be possible. And here is why.
Golems, and thralls as we understand them, are designed only to
mimic life. Pulled from the lore; "Necromancy is not simply the manipulation of dead matter, it is the mimicry of life in unthinking constructs. Most necromancers do not have the time or resources to meticulously craft golems and so most have evolved through the use of the dead." This is very different from the theory of enhancing existing life - which is something more adeptly covered in magics such as Graft, and especially Hone. The theory that using a thrall as armour would provide enhancements to the body is simply not true, unless one was using a Well to power it, as extremely high-rarity wells such as Emetyte produce thralls where "regeneration tends to be remarkably fast and their capabilities will easily be nearly double that of their counterpart." And obviously, containing Wells, these constructs have minds of their own.
This means that in order to create a 'powered suit' out of a Golem, one would need to create something larger than a human - a Fetch , remember, "is a small servant, usually no larger than a toddler. It can be made from clay, dirt, or fashioned wood as a doll." Ordinary Golems "tend to be clumsy and slow by dint of what they are made of, but some necromancers who fancy themselves engineers will design socketed joints and other apertures to make a golem a far more fearsome and quick opponent," and even then, since this would need to be
larger than an ordinary human by a significant amount in order to utilise the abilities suggested, it would need to be a Hulk, which is only available at Expert levels and beyond. To be made of metal and not the "stone, clay or wood" that an ordinary Golem is created from, it would need to also be a Metalborn.
All of this finally ignores the one major takeaway of this problem. The Golem, possessing a Well, would operate entirely independently from the Necromancer as all Welled thralls do, and therefore the Necromancer would not so much be wearing a powered suit, but rather sitting inside the chest cavity of a thrall like a stowaway, while the Thrall simply followed the directives and protocols pre-installed into its core by the Necromancer beforehand. The thrall would need to be thick enough on the surface that it does not simply collapse under its own mass without any internal support structure - and no, the Necromancer does not count, because otherwise the moment the Necromancer exited the thrall, the thrall would collapse under its own weight regardless - and thick enough to be able to act as real armour for the mage within it - but also thin enough to be able to move without being impeded by the Necromancer, and to not overburden itself to the point it becomes incapable of walking, regardless of its enhanced strength, since it is also guaranteed to weigh several hundred pounds and lacks any independent skeletal structure, including socketed joints, which again the necromancer cannot provide unless they plan on being permanently welded to the thrall in question.
I understand and appreciate the interest in looking for out-of-the-box approaches to magic, and I sincerely apologise for the level of detail used here, but I wanted to set something straight here. If an entirely new approach to magic was going to be constructed, such as the use of necromancy thralls to enhance existing bodies instead of creating new ones, that completely diverged from the current parameters of the wikilore, it would require that the practitioner in question be - at the very least - a Revealed necromancer. Not an expert. Certainly not a novice. Because such a thing would be considered a groundbreaking new discovery, worthy of being added to the lore, and worthy of significant merit.
It would also need a very extensive plotline, showing research and study that only a seasoned Necromancer would be able to understand, before simply breaking the mold and doing it their own way.
I hope this answers your question. All quotations are drawn from the Necromancy Lore page, found
here.