I picked up matching jammies for them from Gymboree. Isabel was so excited that she & Henry were "twins". They actually got another matching set as well. The best part is that as long as Isabel doesn't wear hers out he will get them as a hand-me-down when he gets old. Although, at the rate he's growing he'll be wearing these in a year. :)
Next month he turns both 26 weeks and 6 month on Friday. On Thursday he will have his 6-month well child visit and will get a couple more vaccines.