So the depending on your size the best onesie/bodysuit on solid color that I have found is from the abdl store Tykables(issue is they usually sell out quickly and limited non-abdl solid colors also like right now waiting on restock), if your an XL or under Easy Access Clothing (they make high quality clothing for special needs teens and some adults they only offer up to adult xl) I own a few but they changed owners & stop offering larger sizes. I haven't tried these 2 yet but Babykins and on Etsy Bigtot Wear2work both have good reviews Bigtot mainly sells to abdl but they offer probably the most color options where Babykins does offer few colors have heard some have plastic snaps which I haven't used in a onesie but have cloth diapers with plastic and find them better than metal ones
Another idea Duluth Trading company sells regular tee-shirts short and long sleeved that have extra long tails or backend is longer(they market to no plumbers crack)
Both options are good and I have both but even though me personally I am in a wheelchair so diapers poking out isn't really a big issue but is something that I am always checking. Me personally I prefer onesie shirts the best but things to look for is you want ones with high quality snaps that are more forward almost or close to pelvic area it makes them easier to snap with minimum of 4 snaps and a wider panel that comes from the back & snap up front.
Rearz is ok quality shirt but can stretch out also snaps are smaller look like ones used on infant/toddler clothes a d the crotch is sort of narrow also where it snaps is closer to middle of crotch.
A reason I suggest a onesie/bodysuit over Duluth Trading long tail shirts is the onesie will help keep everything in place from abled bodied people I have spoken with they help support diapers. No matter which brand you use when wet they can sag a little and they aid in supporting them.
I personally had a bunch from easy access clothing but they have changed owners they are really high quality but don't offer bigger sizes anymore and I just bought their last 2XL ones they had and their not making them anymore my only complaint if really one they were only offered in limited colors.
Like I said my go to when I'm stock is tykables but only offered in white, black & bright blue(almost royal blue). I will say before I knew about the other 2 I haven't bought yet but want to try them as an alternative, I did buy a solid color romper from tyables basically the same but they snap in middle and almost like tee-shirt short shorts combo(they go down the leg about length of boxers and snap in half moon shape) I will say even though they are a complete pita to snap up on your own if you need to lay down the reason I do like them is and think good option for able bodied person is a normal onesie is shorter where the romper has same protection and features but where they come down thigh like length of boxer I think offers more airflow to crotch area and less material that could case friction.
Sorry for long reply just wanted to give important information I can provide pics of products (by themselves) if needed
Onesie:
tykables.com/collections/snappies/products/black-t-shirt
Romper:
tykables.com/collections/snappies/products/blue-romper
easyaccessclothing.com/collections/disabled-people
Haven't tried ones;
babykins.com/collections/adult-incontinence-clothing/products/kins-onezie-t-shirt-original-12000?variant=31710045667408
www.etsy.com/listing/1108139433/adult-baby-wear2work-bodysuit?click_key=e35710939b0a55e8736fb57e866885d71a02a91c%3A1108139433&click_sum=7e4033d6&ref=search_recently_viewed-5&frs=1&variation0=2286770892
