Petr, I am so sorry to hear about your loss.   Our 17 year old cat passed away earlier this month and it was difficult. A friend of mine said something that I took a great deal of comfort in and his advice was perfect.

He said that we really can't call them "pets", they are our friends and become a huge part of our life. We thank them and give them our love for allowing us to share lives together.

His advice to me was to get another cat when we are ready. It is a way of paying the deceased back for all their kindness - you give an animal a good loving home and they pay you back with great companionship. As a way of honoring them, you give another animal a chance to share the love and safety you gave to the deceased.   

I didn't think we were ready, but we went to a local group to see their cats and ended up coming home with TWO brothers. They have made themselves at home and their different personalities add a great light to our family.   They cannot replace our deceased friend, that is not the point. The circle continues.

Be well. Remember those wonderful times.