Help with sleeves please! Increasing a rib pattern

Hi everyone

I’m wondering if anyone can help. I’m a novice knitter and am knitting a hooded cardigan for a baby. It’s in what I think it’s called fisherman’s rib - the pattern consists of two rows:

  1. Sl1, knit to end
  2. Sl1, *k1b, p (rep. from * to end)

I’ve knitted all the parts for the body, but I’m having an issue with the sleeves.

The pattern says to cast on 29 stitches, then knit the pattern (as above), but to increase 1st at each end of every 4th row until you have 55 stitches on the needle.

I’ve tried every way I can think of to add a stitch at each end, but everything I do throws the rib pattern out so that I lose the rows of ribbing. Should I add the stitch before or after the slip stitch? After adding a stitch do I need to mess with the pattern to change the order of the stitches to somehow keep the pattern in line?

It’s driving me mad! I must have tried to start the first sleeve about a dozen times and I just can’t get it. I’ve tried looking online and I can’t find an answer. I feel like it must be something quite obvious that I just don’t know as a novice knitter! If anyone is able to provide any advice I’d be so grateful (as will our baby so that he/she doesn’t have cold arms!).

Thanks in advance for any help you can give!

Welcome to KH!
You can work the increase sts in stockinette (knit on the front, purl on the back) until you have enough to work another repeat of the rib. Work the slip stitch, then increase and work the rib pattern making sure that you continue the rib pattern in the earlier rows.
After the next increase you’ll have enough new sts to work another repeat of the rib.
What pattern are you following?