I was just looking into something pretty similar. I assume (correct it if it's wrong) that you have a microphone and it is connected to the main console. I don't know what mic you are using and if it has an XLR or TS, needs phantom, etc. Also are you sure you want/need a mixer?
One option is the Boss LS-2 pedal (if you don't need XLR/phantom or can convert). AFAIU you can use a MIX mode where one send/return will have your effects and the other will have your clean tone if you leave it emplty (I think). You can balance them with volume buttons for each.
You can use an A/B/Y box or just a Y/splitter. Pass one through the effects and control the balance in the main console.
You can use a small mixer. I guess you would need one with panning. You then need a splitter and connect it to two channels, one of them passing through the effects. Then balance, pan both to the same side and use that output as your one signal into the main console. If you already have a splitter or somehow have the two signals, just the mixer.
I'm not sure about a mixer but I think there are some really small ones especially for combining signals. They aren't like what a normal mixer looks like, just small box with inputs and output (sometimes vise versa too) with volume for each channel. Something like this (have no idea about quality) http://www.bhphotovideo.com/c/product/141978-REG/DOD_VAC240_AC240_Resistance_Mixer.html
If you give more details about what you want to connect with what etc. maybe advice can be more specific.