You really shouldn't feel guilty @Tammy Cooke. When I was growing up one of our labs was put to sleep, she was only 3 and we were heartbroken. We all said we couldn't get another dog, we were too grief stricken, but coming home to no nose snuffling at the front door or no-one to throw the apple core to when we'd eaten the apple and no little body brushing by our hands when we were sat in the lounge was too much. Within weeks we had a new puppy who, after an initial adjustment period, was the sweetest, softest girl you could ever imagine and she repaired our broken hearts.
Sadie sounds like a fabulous dog and it's a credit to both of you that you have such beautiful memories of her. I agree with everyone else - you shouldn't feel a drop of guilt. The right time is different for everyone. It sounds like your right time is now! I'll put a different spin on the guilt: my dog Brogan (in my avatar) passed away two years ago at this coming Christmas. It has been VERY difficult for me to be ready to move on, and I've actually had people tell me that by dragging my feet to get a dog, I'm somehow not honouring Brogan's memory. Now, I don't necessarily agree with that, but it just goes to show that everyone has an opinion of what you should or shouldn't be doing. I'll tell you what I tell myself: the only opinion that really matters is your own.
We went to search out Coco only 6 days after lovely old Scooby died. We were devasted, but knew we needed another dog to join us - he had left such an imprint on our lives (we also had Belle then). There's no replacing a dog, but we can fill a hole. We have a hole now, but can't adopt until Coco is more reliable. You know what is right for you and your family.