The Problem Solvers Boostinator kit works well enough, but the axle spacers do drop out every time you remove the wheel. It’s fine if you’re not removing wheels all the time and would be the simplest/cheapest solution. Some hubs do have boost conversion kits available, but not many.
What fork are you looking at? I’m guessing you’ve just found a good deal on a non-boost fork?
You could build a custom wheelset, it can be an expensive way of doing things, however it becomes significantly cheaper if you’re happy to build them yourself.
bonus answer: I wouldn’t go much lower than a 25mm internal width. For reference, I’m running DT swiss E512 rims right now – 25mm internal diameter, running 2.5″ Maxxis tires. Works well. They’re a strong rim for not that much cash.
I’d suggest (since this is an initial build) that you try to find a boost fork, unless you found an incredible deal on your fork. Its likely paying the difference in price will save you a lot of headaches down the road if you need to replace wheels. Keep in mind, decent non-boost wheels will only get tougher to find and there’s a decent chance you might end-up buying two forks over the long run.
Full disclosure; I have a boost frame/non-boost fork and am constantly on the lookout for good deals on boost forks for if/when I want/need new wheels…
All tires can reasonably use a wide variety of rim widths.
2.2 tires i15-30 rims (i=internal width)
2.4 tires i20-35 rims
2.6 tires i25-40 rims
2.8 tires i30-45 rims
3.0 tires i35-50 rims
However the i30 rim is the universal rim as it works reasonably well with 2.2 to 2.8 tires. In addition nearly every rim/wheel manufacturer makes i30 wheels. If you stick with boost hubs you can find some amazing deals on wheelsets with i30 rims like the DT Swiss M1900 Spline 30 for less than $500.
However, you won’t find many premade wheelsets with non-boost hubs. Non-boost hubs are history. Getting a non-boost wheelset would likely require a custom build. The extra you pay for the custom wheelset would likely cover the extra you would pay for the boosted fork. Check out ColoradoCyclist.com for custom wheelset prices. If it was me, I would go with boost hubs all the way and get a boosted fork.
In addition, I would want any new bike to have frame clearance for at least 2.6 tires. (All modern boosted forks have clearance for 2.8 tires.) I’ve been riding 2.6 and 2.8 tires for a while now and I wouldn’t want to ride anything narrower ever again. If you’ve been following mountain bike trends, you know many new bikes now come with 2.6 tires or at least have frame clearance for 2.6 tires. And usually, those 2.6 tires are mounted on i30 rims. Even if you go with 2.4 tires, leave yourself the option to use wider tires.
Ideally, at least from my point of view, all modern Mountainbikes would have frame and fork clearance for 2.8 tires and come with i30 rims. That way, the bike could use any tire from 2.2 to 2.8. To the best of my knowledge, only the new 2020 Trel Fuel EX comes this way.
So the fork I was eyeing up sold out but is still available in 29″ flavor. What are the thoughts running 27.5″ in a 29″ fork? The fork can be adjusted to 150mm instead of the 160mm that the bike is designed for, I think the angles should all be good still. Plus and mullet would be in play.