There's still the option of designing your own; I know you don't want to mess around with it, but there's a lot to be considered in such a design (so great for beginners) and it will ultimately cost far less than a DC-DC module.
I started down this track with a DC-DC converter for my General Purpose power supply design, and I found myself enormously frustrated. For a start, it is almost impossible to find a source of the right cores with the right material, right gap, right former and right mounting hardware at a decent price for an open source-type design. The builder would also need to get the right gauges of enameled copper wire, the right tape, and then if they do not build the transformer perfectly, it can ruin both the performance and the safety. A poorly constructed switching transformer can easily result in the supply just destroying itself after a few minutes.
The amount of design involved in a good isolated supply can be an order of magnitude more then a boost or buck converter. When I have done it in the past, it is not hard to end up with about 30 different transformer designs before I get an optimized design I am happy with. An isolated switching DC-DC converter usually works on the bench the first time you power it up, but to get the right power/input/output voltage ranges, the right efficiency, the right noise performance, the right level of switching transients due to the winding leakage inductance, etc is a job that can take weeks or more.
Even more frustrating is seeing the modern core types that could give a much smaller, and much better shielded transformer, except the cores are unavailable if you are not ordering quantities well into the thousands per month. In many cases, the moderns cores require custom pre-formed windings made from flat rectangular-profile enameled copper wire. Impossible for the hobbyist.
All this means that if you try and design an open source isolated DC-DC converter, you are likely to end up in the transformer manufacturing and supply business. As there is safety isolation involved, this can easily be a task you want to avoid.
If you go down the track of using an off-the-shelf transformer, the reliable supply of cheap transformers is pitiful, they are usually very poorly specified (so you have to get them and test them to see if they may work as required) and never exactly what you need. I found that to get the performance I needed, instead of going for a custom 10mm core design, I had to choose a 25mm footprint transformer that was way to big for any compact case. You can be lucky, but usually not.
The DC-DC converter module is just a more practical way to go, and for most people, it ends up being a cheaper option.
Richard.