I think the optician might be trying to save you money in that he believes the eye problems are caused whilst reading and the astigmatism, being slight, will not be causing problems with distant viewing. Single-vision lenses are cheap compared with bifocals or varifocals, so he might think that you won't get value for money out of a full prescription. On top of that if the specs are just for reading they will not be worn continuously nor will you need/want to have photochromic lenses, so you will end up with a much cheaper pair of specs. I think it's worth going with a cheap pair of single-vision specs as the optician recommends. If it works, fine; if not go for the full monty and be prepared to pay a few hundred pounds.