Try doing a loop-on-ground. A 60' circumference (i.e. a square with 15' sides) is a good starting point for a basic LoG.
I would be more concerned with common-mode choking than impedance matching if using a LoG or unterminated BoG as simple impedance is going to be a moving target depending upon frequency. Pretty much any 1:1 choke designed for MW/HF should suffice. Do not spend any serious money. For example, wind some of your feedline through a Fair-Rite mix 31 or 43 torrid, or even a TDK N30 if desired.
Alternatively, I even use inexpensive mix 73 binocular cores and enamel magnet wire to wind basic chokes for low frequency receiving antennas. Four turns for primary. Four turns for secondary. End result is a little 1:1 isolation choke, at least for up to a few MHz. Fair-Rite 2873000202 is under $1 each.
If doing a true *terminated* BoG with a resistor to ground at the far end, then figure around 200 to 300 ohms simple impedance on MW and lower HF bands. A basic 4:1 current balun at the feedpoint should suffice.
All that said, I actually tried various baluns on my 148' LoG over the years. I ended up tossing them and using feedline straight to the LoG. I did have a few snap-on ferrites of whatever mix(es) on the feedline near the feedpoint, plus a KD9SV common-mode choke back near the receiver, but neither did much for my particular environment. Another YMMV situation.