Your wasting your time with this approach IMHO.
In order to work well with bass, IEM buds need to seal. So you need a mix of the band to go with the sound of your bass. Otherwise you will not hear the band well enough to play.
There are IEMs with an ambient sound feature. AFAIK these are very expensive. Ambient IEMs are designed to both give good bass response and allow you to hear what is going on around you. This would be better than nothing, but I still think you will be better off using a mix.
AFAIK an IEM transmitter will require a line level input. So you can't drive one with most DIs. For example, the PSM300 User Guide says the input is switchable from -10dBv to +4dBu: consumer and pro line level.
Probably the closest you can get cheap is a something from Rolls. You can send a vocal mic, line level bass signal, and a line level monitor mix from FOH to the Rolls PM351. You can mix these three signals to taste. The instrument and mic signal pass through to FOH on balanced XLRs.
The down side is the PM351 does not give you any tone control or a limiter to provide protection. You could use a pedal preamp for tone control and to boost the signal to line level. Make sure you get a preamp that can actually put out line level.
With all due respect to your wisdom and experience, @Wasnex (not being facetious or sarcastic, I do value your advice!!!), this is both do-able and not a waste of time.
Case in point: I'm the only dude in my two recent/current bands on IEM. I use them because I have hearing damage and tinnitus and would like to retain what hearing I have left and not aggravate the tinnitus unnecessarily. I also want to be able to hear myself singing - without relying on mains/monitors to hear myself.
Scenario 1: loud three peice rock band. I play bass and sing (backup mostly). I have a need to hear my bass above the loud guitar and drums as well as hear my vox but I don't want to crank my bass either. I use the Behringer P1 with a feed coming from my amp's DI (Ampeg PF500) and an aux mix of the band's vox channels from the mixer. I run my AM Pro 20s from the P1.
Scenario 2: very loud "country-soul" 5 piece. I play pedal steel and sing. Sometimes acoustic guitar. Again using the P1 with a feed coming from my amp's DI (Peavey Nashville 112) and an aux mix of the band's vox channels from the mixer.
In both cases, I want to hear my instrument clearly without overpowering the room and making things even louder. I also want to clearly hear my vox and and the band's vox so as to have half a chance of singing in key. In both cases, I'm able to achieve this.
This works REALLY well and has zero impact on the rest of the band. No need to pass through signal to the board. This is off to the side of the rest of the system. The Westone AM Pro 20s ($239, not the cheapest but not the most expensive, either) are ambient so I don't miss much of the room sound. Just takes it down a few notches of dBs. Actually, I had Shure 315s before the Westones and I didn't have much problem hearing the room even with well-sealed ear buds. Yes, it's just that loud, for better or worse.
So for, under $500 (P1 and AM Pro 20s) and running two XLR cables into the Behringer P1, I am pretty much set. I can hear myself and protect my hearing at the same time.