I love being a Dom in the bedroom and we have a wonderful time but my husband wants more severe spanking but I find it difficult when his bottom gets red
He wants more and more and said he will let me know if he wants to slow or stop but I find it difficult to go too far
any advice on how to overcome the fear of hurting him
Very common situation. As a sub to my wife , sometimes , I’d love her to spank or whip harder . In “subspace” a sub can be crying out in agony, yet not want the punishment to stop . Best thing is to have a safeword , a common one is the "traffic light " , where Green is carry on amber is nearly there , and Red is STOP .
Spank /cane / whip , whatever . No matter how Red his bottom is getting , he will tell you if he wants you to stop .
I promise , give him a spanking to remember, and he will love you for it
Enjoy !! 
Keep communicating. Express these exact thoughts to him and talk about it until you feel comfortable. Safe words/actions should be in place and discussed often. And you never have to do anything that you are not comfortable with. You both should be able to enjoy playtime. Pushing limits is one thing, feeling bad about part of the encounter, regret, guilt, can ruin future adventures. Communicate. Best wishes for a successful scene.
I often read how partners concentrate only on the limitations of the submissive partner. This notion is erroneous as it assumes that the dominant party is entirely in control of the scene, negating the need for them to express their limits.
It is essential to note that both the dominant and submissive partners can have boundaries and limitations in a power dynamic relationship. For instance, there may be certain phrases, titles, or dynamics that the dom or sub prefers not to be used or involved in, or there could be activities that the submissive partner desires but the dominant partner is not comfortable engaging in.
It is imperative to understand that power dynamics can be equally, if not more, vulnerable for the dominant partner. The misconception that only the submissive partner is susceptible to harm can be dangerous for all parties involved. As such, it is advisable to ensure that aftercare is provided to both partners, not just the submissive.
Additionally, if a safeword is utilized, both partners should be informed of their ability to invoke it. Regularly check in with each other about boundaries and to acknowledge that dominance is also vulnerable. Communicate how you feel about more intense spanking when both of you are outside of the bedroom. Check in with yourself to understand if you are willing to push your own limits or if you need some time before stepping outside your comfort zone. Good luck!!! 
We have more than one safeword - so we have clear options for slowing down or less hard, as well as stop.
I like incorporating a sub doing things to themselves into a scene - in part as a slightly hotter way of establishing thresholds etc - but following communication.
He does wear knickers during the spank but he likes me to pull them down during the spank so I don’t think this will work - but thanks for your input
It’s my head - I need to accept it’s his fun
I guess just have safe word and or safe gesture. But sometimes you might not be able to overcome your fear of hurting your partner.
My husband has a pretty good idea of how much I can take, so he’s the one I go to for my dose of sexy pain. My GF, on the other hand, can only do the lighter stuff. She’s scared of hurting me…says I’m too cute. 
There is only 1 time he asked me to stop and that was after I had an argument with my mum and I was angry and so I took it out on his bottom .
We have safe words (traffic lights) but it’s me I just need to accept he wants a sore bum - he wants to feel the sting
I just need to work on it-
When I’m being a Dom in the bedroom I dress the part and I take on a different persona- this allows me to be a dominant woman and then I find it easy to spank him like he wants.
You need to get into a different head space and just go for it 
Maybe try a safe word so you both know if it gets too much then you can activate it 