Idk if it'd be too late, but better to say than not...
... I'd definitely recommend going with premium underlay. That's what we used to have/replaced and we just went for one of the cheaper ones when we redid the stairs and landing. Definitely a mistake.
Money gun was definitely aimed squarely at "best undrlay". Our thought was if we're going carpet, it's going to be as plush as possible. Especially in mini_com's room to try and take something away from her thundering around on 100 year old suspended flooring.
Idk if it'd be too late, but better to say than not...
... I'd definitely recommend going with premium underlay. That's what we used to have/replaced and we just went for one of the cheaper ones when we redid the stairs and landing. Definitely a mistake.