Best pattern to return http responses with observables

I'm writing a server in TypeScript, and searching the web I haven't found much about writing a controller that returns an http response using observables. I have a draft and it works, but I wonder whether this is the correct approach especially in the long term, or there are better patterns that I could follow. In My controller I return a promise from a service:

  public getUser = (): Promise<User> => {
    return this._service.findById('id');
  }

The service :

  public findById(id: string): Promise<User> {
    return this._repo.findById(id).pipe(
      map(res => res ? Response.ok(res) : Response.notFound(`id: ${id} not found.`))
    ).toPromise()
      .catch((err: Error) => Response.internalServerError(err));
  }

and the repo:

  public findById(id: string): Observable<User | null> {
    return from(User.findById(id));
  }

Once it comes to write longer functions in my service I could create a new observable, do the logic in there and then return the result as a promise. What are your thoughts? Can it be improved? Thanks in advance