The 5V from the USB should be stable. I'm not sure why you think you need a boost to be honest. Even if you did need 5V, I thought you would want a SEPIC or buck-boost or something that can bring both higher and lower voltages to 5V. Is the boost converter only there to make up for the Schottky diode's voltage? If so, don't use a Schottky; Use a PMOS circuit.

The OP's circuit here will work if you just need the USB to override the battery whenever the USB is plugged in. It prevents the USB from injecting current into the battery. It is simple but does not accommodate battery charging:  Is this MOSFET upside down?.

This is why just a PMOS alone won't work in many two-supply situtations: nmos reverse current protection.

Lastly, this here makes a true ideal diode with an PMOS that behaves in the way you take for granted with a real diode where any and all reverse currents are blocked irrespective of circuit voltages, and does generally work in two-supply situtations:  Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors

You do not need this last one for your battery-USB function if you just need the USB to override the battery and not discharge into the battery. The first circuit works for that. But the very first circuit might not be applicable if you want to actually have the USB run through a charger for your battery. You may very well need something like this then.

You may also need it in other parts of your circuit since I see multiple Schottky diodes. But just use Schottky diodes if you can tolerate the voltage drop. Much simpler.

The 5V from the USB should be stable. I'm not sure why you think you need a boost to be honest. Even if you did need 5V, I thought you would want a SEPIC or buck-boost or something that can bring both higher and lower voltages to 5V. Is the boost converter only there to make up for the Schottky diode's voltage? If so, don't use a Schottky; Use a PMOS circuit.

The OP's circuit here will work if you just need the USB to override the battery whenever the USB is plugged in. It prevents the USB from injecting current into the battery. It is simple but does not accommodate battery charging:

Is this MOSFET upside down?.

This is why just a PMOS alone won't work in many two-supply situtations: nmos reverse current protection.

Lastly, this here makes a true ideal diode with an PMOS that behaves in the way you take for granted with a real diode where any and all reverse currents are blocked irrespective of circuit voltages, and does generally work in two-supply situtations:

Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors

You do not need this last one for your battery-USB function if you just need the USB to override the battery and not discharge into the battery. The first circuit works for that. But the very first circuit might not be applicable if you want to actually have the USB run through a charger for your battery. You may very well need something like this then.

You may also need it in other parts of your circuit since I see multiple Schottky diodes. But just use Schottky diodes if you can tolerate the voltage drop. Much simpler.

You need OP's circuit here: Is this MOSFET upside down?.

This is why just a PMOS alone won't work in many two-supply situtations: nmos reverse current protection.

Lastly, this here makes a true ideal diode with an PMOS that behaves in the way you take for granted with a real diode and does work in two-supply situtations: Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors

However, you do not need this last one for your battery-USB function since you have a specific use case between USB and battery here that works itself out. That use case is that you never need the PMOS to block the battery from discharging into the USB)

However, you may need it in other parts of your circuit since I see multiple Schottky diodes. But just use Schottky diodes if you can tolerate the voltage drop. Much simpler.

The 5V from the USB should be stable. I'm not sure why you think you need a boost to be honest. Even if you did need 5V, I thought you would want a SEPIC or buck-boost or something that can bring both higher and lower voltages to 5V. Is the boost converter only there to make up for the Schottky diode's voltage? If so, don't use a Schottky; Use a PMOS circuit.

The OP's circuit here will work if you just need the USB to override the battery whenever the USB is plugged in. It prevents the USB from injecting current into the battery. It is simple but does not accommodate battery charging: Is this MOSFET upside down?.

This is why just a PMOS alone won't work in many two-supply situtations: nmos reverse current protection.

Lastly, this here makes a true ideal diode with an PMOS that behaves in the way you take for granted with a real diode where any and all reverse currents are blocked irrespective of circuit voltages, and does generally work in two-supply situtations: Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors

You do not need this last one for your battery-USB function if you just need the USB to override the battery and not discharge into the battery. The first circuit works for that. But the very first circuit might not be applicable if you want to actually have the USB run through a charger for your battery. You may very well need something like this then.

You may also need it in other parts of your circuit since I see multiple Schottky diodes. But just use Schottky diodes if you can tolerate the voltage drop. Much simpler.