Selecting gate driver for smps
I searched "nmos high side driver dip" on google and found a number. The IRS2117PBF should work well. Also check out the other chips from that google search.

In terms of using an IC with feedback, I'll need more details about the limitations of your project to give a good answer. If custom means that you need to design the basic buck circuit by hand, you can get buck controller ICs that don't include the switch. For example, you could use a LM3489. It includes the feedback and gate driver circuitry. You'd implement it like so and just have to add a couple components to what you have so far to get it working...