Sleep Sack? Summer? Blanket?

Ok ladies I need advice google is failing me, haha. So our sweet girl is about to outgrow her sleep sack which is perfect because they are fleece and summer is quickly approaching. I just wonder if I should invest in bigger summer ones or just try and transition her to only pjs. My fear of just pjs is right now when we put her in her sack she knows it's time for bed. So how would we make this transition? Also she's going to be 9months soon could I just give her a Muslin blanket? She is a very active baby standing, crawling; I believe she would do fine with a blanket. Any advice? Thanks so much!