I had a similar need regarding the instrument switching and after much reading, pricing & debating this is what I ended up doing for many reasons. Namely, the work, time, and materials involved did not stand up to this pro-quality product for the price.

Note regarding the price. You may find a used model on Reverb?

Inaudible instrument switching: The whole point of the Lehle 3at1 SGoS instrument switcher is that your audience shouldn’t know you’re switching instruments without seeing you do it. That means no pops, no clicks, no hum while you grab your next instrument. Just leave them all connected to the Lehle 3at1 SGoS, and it’ll take care of the switching silently and reliably. How? Gold-plated relay switches with pop/click suppression – professional grade circuitry for serious performance.

Mix and match instruments and sources: You may have found the Lehle 3at1 SGoS looking for a solution for your guitars or basses, but it can handle virtually any instrument with ease. Acoustics with piezo pickups, passive or active pickups, and even line-level sources are accommodated by the 3at1 SGoS. And inputs A and B have gain adjustments, so you can balance all connected instruments and sources relative to input C.

• Silent switching for up to three instruments
• Versatile inputs handle electric instruments, piezo pickups, and line-level sources
• Gold-plated relay switching and pop/click suppression provide sonically transparent performance
• Stereo signal path makes it ideal for stereo effects processors
• Programmable via MIDI for configurable functionality

https://www.sweetwater.com/store/detail/LE3AT1

That said please comment with other suggestions if you have them.