http://www.mamasource.com/request/6828390721557364737
Above is the link about double strollers, which was a question asked in MamaSource not long ago.
For books, just go to www.amazon.com and type in the search word "big brother books." Many will come up and you can see the reviews.
As for your son, he will be 2 years old when baby comes, right?
Main thing, is to talk with him about it & LET him express himself about it with no judgment or criticism, and likewise, whether for good or bad moods. 2 years old is a hard age... and in fact 2-3-4 years old is hard developmentally because they are changing so rapidly and transitioning in many ways. Just keep your 'routines' for him consistent and this helps a great deal.
As for books, I just went to the bookstore and picked up a couple for my daughter when I was pregnant with my 2nd child. But in reality, the books were okay...but mostly, my girl just got the 'big sister' thing just by us talking with her about it, and exploring things and her feelings. At 18 months old... they will not yet grasp the concept of being 'a big brother' because it is an 'abstract' concept... and developmentally, at his present age, it might not get comprehended literally. And yes, the attention span at this age is different, than an older child. But it's always good to read to a child, and its a nice one-on-one time with him.
Or an alternative would be to get him an age appropriate video about it.
As far as moving him into a toddler bed... will he be in a room of his own? Or having to share it with baby? Keep in mind, that if baby is in the same room, you will have 2 different sleep patterns/problems/issues going on at the same time. Some eldest children adapt to it, some don't and need their OWN routine/room.
Getting him IN a toddler bed is one thing... then him getting adjusted to it, is another 'phase.' Be prepared for a toddler getting out of bed, 'escaping', coming into your room... not wanting to sleep 'just yet,' dilly dallying etc. And if he will be potty training at the same time... well, that is a LOT for him to adjust too... along with having to adjust to having a baby, having his Mommy be busier, and having to be in a toddler bed. Many developmental things to keep in mind, and the 'emotional' aspects to it as well.
But, some have done it this way. Each child is different. Just gauge him. Go according to HIS readiness. Or he may feel 'forced' and pushed out/away....and all because of 'baby.' Then again, some toddlers have no problem transitioning. So just see how he does. But do not 'force' or punish... there is no reason to do that, or he will think going to bed is a torture and not like it, or resent the 'rush' for him to do so.
So many things to thing about. Just keep things age appropriate. VERY important. Key word. Many times, once a 2nd baby comes, the now eldest child is indirectly expected to 'be' and 'act' older than they are, and they get stressed out, regress, tantrum etc. because they don't have 'coping skills' at this young an age.
SORRY for rambling... I got off track! Didn't mean to... I'll stop now.
All the best and congratulations,
Susan