I am decidedly anti-acrylic. There's something about the feel of it that just makes my teeth hurt when I touch it (I know...that's really strange). Washable wool is lovely. I've made a few things with that for this babe so far. I've made some from regular old wool too (just as I have for DS). I like some bamboo fibers, but they are pretty highly processed though sort of natural. They are often nice and soft and can be machine washed (depending on what they are blended with). I'm generally not a huge fan of knitting with cotton (not to say I never do it) but most of those items, while they can shrink some, I go ahead and wash and dry in the dryer. I actually don't like cotton sweaters (or the like) to be line dryed or flat dryed as they seem to loose some softness (but maybe that's just me). I'm also not totally opposed to using some washable wool blends that have a little acrylic or nylon in them, but I never want that to be the primary fiber (sock yarn for instance can be a nice weight for some baby items). For wool, It does just become a matter of knowing which items are which and I keep a separate hand-wash basket for non-washable wool items and do a batch of hand-wash once I collect a few things in there. Really, I don;t feel like it takes that much time. As for convincing your MIL, I don't know what to tell you. Try compromising with washable wools and some blends? If you want to do any wool diaper covers/longies though, washable wools and blends are not good for those.
Plastic gifts are a whole other story. It has literally taken 3 years to get family members to stop getting them for DS. We by and large do not keep them, or we leave them at grandparent's homes as toys to play with there. My MIL just at DS's 3rd birthday seemed to realize that we haven't kept any of the plastic toys she's given and gave him some nice gifts(that DS, DH and I all loved). As a baby, I'd say let your child play with whatever when it's first given, if the giver is present, and the once they leave, take it away and donate it. Most babies aren't that interested in toys anyways for a while. It gets harder as the child gets older and wants to keep said toys. Generally, we'll keep things for a week or month until DS looses interest in it and then I take it out of rotation and donate it. I hate when he gets plastic gifts because it feels like people are wasting money on things we don't want him to have (and are not going to keep), but at the same time I try to accept them with grace and focus on the love with which they were given. This has been a real process for me in coming to terms with it and I literally spent DS's birthdays/Christmases and other gift giving times with my stomache in knots for three years.
It also has depended on who is giving the gift. Early on I was very comfortable saying to my mom that we wanted toys made from natural materials and enlisting her help in making those toys. We've had so much fun with sewing Waldorf dolls, dying playsilks and even building a wooden barn together (neither of us had ever done any woodworking before). My mom's not big on plastic toys anyways so that helped too. I don't have that kind of relationship with my MIL though, and she'd never dream of making a gift so that was much more difficult.
This year I did make an amazon universal wish list that I gave to family members for DS's birthday and Christmas of things we'd like him to have. I try to include things that can be ordered online and some which I know are available in stores to give folks options. Grandparents especially loved this. They want to give things they know he will love and use and that we approve of as parents. I'm going to probably make a similar wishlist for this babe. The other thing I did was to secretly have catalogs from lovely natural toy companies sent to family members. Some like to buy from them some don't but it doesn't hurt to put the companies on their radar.
Anyways, I hope that helps some!