CDG to the 7th Arrondissement

A taxi is a fixed rate of 58€ to your Left Bank hotel.

If you didn't like the bus to the metro, I don't imagine you will like the RER to the metro -- so this is the time to spring for a taxi.

Vote #2 for a taxi. Very easy, very safe. Go to the official taxi rank in the airport. When you exit baggage claim/customs area look for the signs to Taxi and go get in line. The line manager will wave you to a taxi. Have your address typed out for the driver. I usually tape it to a 3x5 index card.

If the budget for the taxi is a problem, you can also take the Roissybus, it serves all terminals and goes to "Place de l'Opéra". The price is €13.70

Place de l'Opera is certainly a nicer bus terminus than Gare du Nord

From Place de l'Opéra, taking the metro line 8 (direction Balard) you will be 3 metro stops from the 7th arrondissement.
first station in 7th is Invalides, the next station "Commerce" is also in the 7th arrondissement.
You can buy a metro ticket in the station - €1.90

I don't know where your hotel is but from one of these two stations you will be close to your hotel (less than <1/4 mi)

Info, map and schedule:
https://www.parisaeroport.fr/en/passengers/access/paris-charles-de-gaulle/public-transport/roissybus

Even as one who avoid taxis if all possible, the ride into Paris from CDG is the #1 exception. The cab to your hotel is well worth it.

Just returned last week from Paris. We used Easy Go Shuttle…great experience. This is the second time we have used them for round trip transfer from CDG. If you are going to pay for a taxi consider this service. Booked on their website, arranged private car, called me when I landed while I was waiting for my luggage, waiting with sign with my name when cleared customs and exited. On the return driver texted me night before to confirm return pick up at hotel at 5:30 am. $65 euro each way, paid in cash to the driver, only a bit more then cost of a taxi. After a long flight comfortable private car with water waiting directly to hotel and timely pickup.

Thanks for the suggestions. I think I'll try the RER B on the way in, to see if I can do it by myself, then take a taxi or car service back the morning of my flight.