1- use a 3v3 arduino and 3v3 sensors
you only need to convert your lipo voltage to 3v3 and you don’t need a level converter for I/O
you can use something like this (called buckboost)
you find many of these boards- step down step up buckboost ect
input from 0.8 to 6 v -> output steady 3v3
so if you drain your battery to say 2.6 v… the output is still 3v3 and your arduino still works.
if you connect your fully charged battery @ 4.2 v also the output is 3v3 no problemo
2- use a 5v arduino and 5v sensors
use 5v I/O sensors and you don’t need a level converter
you need a so called boost module to make the 5v from the lipo
best is then to choose a combination of dc dc boost converter and lipo charger.
now you can leave your lipo attached to the device and plug in an adapter to charge
3- a mix… 5v arduino and 3v sensors / 3v3 arduino and 5v sensors
then you make it yourself difficult
add an extra dc dc converter from 5v to 3v3 so you have the 2 voltages needed for the levelconverter board
* I didn’t search for the cheapest dc dc ect. also depends on the capacity they can deliver