I agree with all the previous posts. It all comes down to technique both lathering and straight razor. I have Van Der Hagen deluxe in my shave soap rotation. It's a good inexpensive soap that when lathered correctly gives a nice slick glide. Don't get discouraged it all comes in time. I've included a link to Shaving 101 that has a good explanation on lathering Mitchells Wool Fat. It may help you with the Van Der Hagen.
Mitchell's Wool Fat Shaving Soap