"shopping" questions are off-topic, so instead I will explain how to do the search, so you can do it yourself next time.
You need a chip to convert 1.8V to 3.3V levels, presumably CMOS. As explained by Janka in the comments, this is not a DC-DC converter, the proper name is "level shifter" or better "logic level translator".
There are many different designs, the simplest are simply open-collector or open drain transistors, but these require pullup resistors which create a compromise in speed versus idle current. For faster switching you need a low value pullup, which then draws lots of current even when not in use.
Your high bit rate would be better handled with a chip dedicated to voltage translation, which will be low power and high speed.
Click the usual suspects: "in stock", packaging "bulk, cut tape, tube" since you don't want a reel of them, then apply filters.
Now you need either one chip with 2 bits, one bit in each direction for your serial port, or 2 chips with one bit each. Problem with the first solution is that most chips with 2 bits will have both in the same direction. Anyway, I will click:
"number of channels" = 2 (presumably one channel is one direction, you need both directions)
"circuits per channel" = 1 to 4 because we don't want a package with too many pins.
This one comes up, in easy to solder SOIC, it has 2x2 bits and you can set the direction independently for both, so you could have 2 extra lines if you want. If you want only one bit try this one.