We are going to Paris in February and would like to stay somewhere very romantic and special. After some research I am undecided between The Marais and Boulevard Saint-Germain. I am looking forward to walking along the river if it is not too cold and rainy. If you have any recommendations of hotels, please let me know that too.
We've stayed in the Marais twice and like that it's lively, close to sights (and not too far from the river) and feels like real Paris. Rather than a touristy area.
We like this hotel and really appreciated their service once when we were sick over a holiday weekend. The front desk staff spent about 45min calling doctors/clinics to find someone who could see us on a Fri evening. It's quaint with a flowery/stately vibe. I would call it romantic. (it also has a cat in the lobby we enjoy saying hello to) The morning breakfast, which is excellent, is served in the limestone cellar. We normally do a quick breakfast
at cafes but always take this breakfast when in Paris.
https://www.hotelparismaraisbretonnerie.com/en/
We've never stayed in Saint Germain so can't compare it. We were last in Paris in April and the river was quite windy some days, so your walking may be hit or miss. Good luck!
Marais area is perfect spot. Having lived in Paris for several years, Feb weather is Feb. weather. Bring layers
Both areas are great and both have a lot of tourists. What is your budget? There are a lot of good hotels in both neighborhoods. Here are two, one in Saint Germain, and one in Le Marais that I have enjoyed.
https://www.hoteldavinciparis.com/en/ (Saint Germain)
https://en.pavillon-de-la-reine.com/ (Le Marais)
I will always choose St Germain, watch YouTube videos of both areas and decide
Leaning more towards the Marais these days thanks to a more interesting selection of shops and restaurants, but Saint Germain des Prés has some superb hotels like Hôtel d'Aubusson on rue Dauphine.
Both are such wonderful areas, I can see why you are having a hard time deciding! Have you ever used "street view" on google maps to "walk" around? I do that to get a sense of the area I am looking to stay in. More times than not that helps me decide which neighborhood I like more. Good luck deciding - you really can't go wrong with either one!