Suggest Dosage Of Injection 'clexane' For Deep Venous Thrombosis

I am a 71 year old man,born and living in Venezuela, 110 kg weight and 177 cm height. I am a patient of deep venous thrombosis (left leg and partially right leg) since 2004. I take every day warfarin (1x 5 mg) and daflon (2x500 mg) and use permanently compression stockings. I am going to fly to Spain, about 9 hs flight. My doctor told me last time in such case I must inject clexane before the flight. My question is: Should I take an injection of 20 mg, 40 mg or 80 mg clexane to myself just before the flight?
Please, I would like to know your opinion.
Best regards,
José Montero
Caracas, Venezuela