If there is no particular structure in your practice you should have one.Probably good idea would be to follow a system such as AYP or Kriya yoga sadhana.AYP is right here in the reach of mouse pointer,so you could try it and see for your self does it suit you.Obviously,AYPers of this forum are ready to jump in and help you.
Kriya yoga is bit different as it requires to go for initiation.Meaning you would likely need to travel somewhere in order to learn Kriya from qualified Acharya,and later on cope with scares amount of support which is quite typical for today's Kriya organizations.Also Kriya requires some serious commitment as sittings can get really long,that is 4-5+ hours per day within first year of practice,in case you are really serious about it.
Kriya Pranayama/Spinal Breathing Pranayama is really stable and safe thing to do.At least in my experience,which includes practice of other Kriyas combined with Kriya pranayama.Probably you would be on safe side as long as you follow instructions found in AYP lessons. And i am quite sure that those 5 minutes of SPB as Christi suggested wouldn't do any harm whatsoever. Just take it easy,have a routine,relax and enjoy:) Spiritual journey towards Eternal Tranquility is best and most important journey one can embark on. Best!
Thanks all of you for encouragement and useful tips. I guess I will give it try and take it really slooowly. And in case I'll get into trouble I will give you a cry for help. Thank you very much, I really appreciate your words.