What a generous and loving heart you have! Your willingness to hand-make something beautiful for your bf and learn to knit to do that is a terrific thing! And everyone here will help you all we can.
You've come to the right place! The videos here, and the great folks in this forum, make this a knitters paradise!
First off, I agree with the suggestion about using Caron's "Simply Soft". I've made 6 afghans with it for my family and they all love them, they're so beautiful and soft and squishy! Also, the skeins have 7 oz. in them so the yarn goes a long way.
You could actually do strips of "garter stitch" which means you'd knit every row. I'd recommend strips since they're easier to sew together than individual blocks. You can even change colors within each strip (Amy has videos on here that will show you how) for multicolored. Or you could do different colored strips. Whatever you envision you can do.
And consider making your strips longer, say 60 inches or so, with a total width of the afghan maybe 40" or 45". That way you can both cuddle up under it. There's nothing like a cuddle-type afghan for warmth and comfort (and romance!).
And don't worry about your time limit. If you're working 2+ hours a day on it, and it's all knit stitch, you'll amaze yourself how much you get done! Besides, since you have such a strong and good purpose, it'll inspire you to keep going and get 'er done!
Good luck with it and please let us know how it's going or if you have any question.
Happy knitting and Happy New Year@