Hi coeanblue22,
I don’t have any personal experience with a of the products you are mentioning and hopefully one of the members that does will see your post and share their experience but I can make a few comments about them that may be helpful.
There is also more about mattress encasements in post #2 here that may be helpful as well.
Organic Cotton Dust Mite Bed Bug Mattress Cover Encasement from healthychild.com
This has a pore size of 4.91 microns which would be suitable for allergens and it also appears to have a zipper that is designed to prevent bed bugs from getting through so this would be suitable for both allergens and bed bugs. The National Allergy Supply description here (they own the bugshield trademark) lists this as 4.8 microns but that is close to the same.
Organic Cotton Allersoft Mattress Encasing from iallergy.com.
This also appears to have a pore size of 4.91 microns but they don’t mention anything about bed bugs or a zipper system that would prevent bed bugs from getting through so this one may only be effective against allergens. Other than this they appear to be very similar.
Neither one of the mattress encasements would be water resistant so if this is also important then as you are suggesting it would be a good idea to use an additional water resistant or waterproof mattress protector on top of this. This way you could keep the allergy/bed bug encasement around the mattress on a semi-permanent basis and remove the protector on a regular basis to wash it. There is more about the pros and cons of the different types of mattress protectors in post #89 here.
I’m also not familiar with this mattress pad but I would personally prefer to have wool inside a quilted mattress protector and cotton as the cover rather than cotton batting with a wool fabric because wool won’t pack down as much as cotton and is more water resistant and temperature regulating as well
Congratulations on your new futon mattress as well 
Phoenix