Attic insulation - very low height

You might talk to an expert, I don't think blowing in insulation would cause the problem of blocking anything off.

You can get the loose fiber insulation and rent a machine that blows the insulation into tight spots. Available at Lowe's and Home Depot.

look into spray insulation!

Before blowing more insulation in, I would have a pro come evaluate. Too much insulation is just as bad as not enough. You can remove what you have and install a modern more energy efficient insulation that requires less space and provides "breathing room."

I think you should have someone professional come and look - even if they only give you an idea of what you'd need, and you DIY the solution!

The call in the expert is good advice-the problem is finding the expert? I have to ask why do you think you need more insulation? People are under the misconception that more is better is not always true. Insulation is the most effective when it has air space in it or NOT compacted. Are you trying to insulate for cold climate or hot? Have you investigated air leakage in and around windows and doors, have a crawl space? or on a slab? Do you have Central air and heat ?

I owned an HVAC business for years and finally figured out even using the computer program to calculate heat load (which includes how much glass facing which direction ,etc. ) I had occasions when a door test revealed a very "leaky" house and with existing duct work either not properly installed or again leaky was a problem that the computer program could not anticipate. Bottom line you can spend a lot of $$$ throwing "solutions" against the wall with negligible results. There are home inspection companies used by insurance companies to evaluate the value of a home by the things I mentioned above plus electrical, plumbing and general condition. I guess if it was me I would start with my Home insurer and get some recommendations. If he/she is ignorant to this idea I would consider finding a new insurer.

A GOOD Installer can get blown insulation where needed. When you mention air flow-do you have a ridge vent or Turbines or the dreaded Power ventilator? The two story dilemma is common. Air has some funny properties like when heated it rises so the hot in the summer is normal and very hot in the winter when you make the 1st floor comfortable. Zoning A/C systems was all the rage for several years but I have found that using mini-splits to be more effective than re-routing the duct work for zoning in most cases, especially if the 2nd floor is occupied as active living space. The new heat pump mini splits are getting very competitive price wise and are 100 % preferable over a window shaker( No I don't sell or recommend brands ). Finding a reputable HVAC Installer is more important than a Brand Installer by a factor of 1000. The Top of the line, most advertised units on the market are Junk if the installer's reputation is Junk. My advice is when you find what you consider to be a reputable Company, Get your quote and ask for the names and phone #'s of his last 10 installs, with dates of install. Many will tell you I can't do that because it would invade the persons privacy. B/S ! I installed for 20+ years and I always obtained permission from my Customers to be able to use them as references. I was Never turned down and still have several hundred on file. Good Luck on licking your problem.

Honestly I would remove the old insulation and have a professional spray expanding foam insulation in there. That stuff seals everything great.